Given the advent of various tablets, netbooks, and ebook readers which works best for viewing AND using roleplaying PDFs. Unreleased products should be mentioned as well as the field is constantly changing. Note that this question is slightly different than which is the best products overall. This should be focused on what works well (or not) for the gamer at home and the table.
The smaller sized Kindles aren't great for PDFs; they're a little bit slow and the screen size is a big issue for most roleplaying PDFs. I haven't tried the Kindle DX, but it's designed for PDF reading so I assume it would be better. However, you're going to run into trouble if you read a PDF designed for color.
I have an iPad, and it's a superb PDF reader. GoodReader is the current champion of PDF readers; it's very fast, it has a lot of ways to get PDFs onto the device -- including downloading them from Mobile Safari -- and it includes a full implementation of folders so you can organize your PDFs. DiceBook is also worth mentioning, since it includes a built in die roller, but it's not otherwise as full-featured as GoodReader.
In my experience using the iPad for gaming, I get the full 10 hours promised by Apple, which is enough for even most convention usage. It's definitely not up to the standards of the Kindle, but practically speaking it's pretty good.
When Android tablets come out in the same form factor, I imagine they'll be just as good as the iPad. Watch out for battery life, though. Apple's using some clever technology there and I think that'll be the hardest thing for Android tablets to match initially, although I'm sure they'll get there in the end.
I do not like the iPhone for anything other than emergency PDF reading, for the same reasons as I don't like Kindles. The screen is too small. Same goes for other smartphones, with the possible exception of the new Dell Streak. It has a huge screen, and is probably worth considering.
I use an Asus 10" Windows tablet for my gaming these days. I use it to read pdfs (e.g. when running a game of Pathfinder from a PFS scenario), and to read and write on pdf character sheets.
I use the 4e Character Builder on my home desktop to build characters, and then CutePDF to create a PDF version of the character sheet, which I move to Dropbox, allowing it to automatically download to my tablet. I do much the same with PCGen for Pathfinder characters.
I use the application xournal to open the pdfs on my tablet, and enable 'writing' directly onto them. This allows me to take notes, or manage current hit points or powers used in much the same way as a physical character sheet. Although there might well be rpg-dedicated apps for doing this, xournal has the advantage of working on ANY pdf, regardless of source, and it allows me to write what I want where I want, without having to pay for a PDF-creator.
I do find that glare can be an issue in some cases, but I'm generally using it indoors, so not as much issue as it would be if I were travelling. I also find that scrolling to graphics-intensive pages (like maps, for instance) can be a little slow. Other than that, I'm reasonably happy with the experience so far. Battery life, with an extended battery, is about 5-7 hours, although the venue I game at has power available.
I also have a Windows Phone (Lumia 920), and apart from being able to web browse to rules reference sites, I've been able to find a Pathfinder Spell database and a 4e power database, both reasonably complete.
After moving from a Kindle Fire to an iPad, I can say with some surety that the killer app for electronically reading RPGs is GoodReader for iPad. I searched high and low for an Android PDF reader with the power and performance of GoodReader, but never found one. Here are the features that I love about GoodReader that I could never find anywhere else:
Excellent file handling
GoodReader can grab PDFs from Safari, from URLs, by browsing for them, or through truly excellent integration with every popular cloud storage service (Dropbox, Box, Google Drive, Skydrive, SugarSync, off the top of my head).
Whenever I buy a new game PDF, I just drop it into a cloud-synced folder and then I can get it onto my iPad whenever I want to.
GoodReader handles zip files, folders, and file management operations beautifully. It is easy to move files around internally, as well as upload them to any of your cloud services and email them.
Speed and quality of rendering
GoodReader is by far the fastest rendering PDF reader I have ever used - especially important for reading highly-formatted and highly-designed files like RPGs. The engine caches a page ahead, so while you are reading you can naturally flip pages at the highest possible speed.
It also handles the most complex and largest files - The Dresden Files RPG "Your Story" book is pretty hefty, and the Marvel Heroic Roleplaying has some complex masks that used to render properly on only the miserably slow Adobe app. GoodReader handles them both with aplomb.
GoodReader supports bookmarks, notes, highlights, annotations.
It even has the unrivaled Crop Margins feature that lets you remove the unnecessary and cumbersome exterior whitespace some books have. I looked for this all over the Android space and never found it. This was the first thing that pushed me to being a GoodReader fan.
It is GoodReader that prompted my switch from the Kindle (and Android in general) to the iPad. A retina iPad is an awesome reading experience - I don't even miss my regular Kindle for long-form text (novels, etc.) anymore.
The full-size iPad is suitable for reading even 8.5 x 11 or A4 formatted documents on, in a whole-page visible manner.
In the 2+ years since I made this comment, I have run several games with just a few printed sheets for reference, using the iPad as I would have used a book in times gone by. I still love books, but I don't print them just on principle anymore.
There are two considerations for gaming that aren't present for normal books, when using an e-reader.
I have tried a few readers, and have settled on the iPad - the screen is big enough, it's fast enough to render pages, and it is easy to use. The other readers I've tried have been great for reading books but too hard work for using for reference.
Update: I still use an iPad and am very happy with it, but i've moved from the built in PDF reader which had trouble on complex pages to Goodreader, which is fast and effective.
I know it's not what you asked, but I use an Eee PC netbook for my gaming PDFs and it works great. Not to mention the ability to flip to an open internet window for other things. The battery life is a bit less, I only get about 3 hours, but usually where ever I am gaming has an outlet and I just plug it in, no biggie. I got mine for less than $200 and I love it. I have bought several pdf rpgs and I wouldn't trade it for the world. I have the books, plus everything else I might need right there.
I bought a Nook Color for that very purpose, but I found the PDF reader that came with it to be barely usable (no bookmarks, no search feature). I ended up rooting the tablet just to be able to load DocumentsToGo.
Configured this way, it's a decent reader, although screen size is an issue (I find myself displaying half-pages, so there's more scrolling). Speed of response is so-so; graphics-heavy pages can take up to 5-8 seconds to load.
I'm currently vacillating between picking up a Motorola Xoom or waiting for the HP TouchPad. Either one addresses the screen size issue, but I'm not sure what the TouchPad will have available for PDF reading.
I have a Barnes and Noble Nook. (not the Nook color, the original E-ink based eBook reader) I would not suggest using it for several reasons.
I've use Sony Readers, and Table PC's but none have really worked the way I want, to slow / to small, I am going to try a HP TouchPad, when mine arrives, as its the same form factor as the iPad, but I'll also be writing some custom software for it to help me manage the Game.
My girlfriend has a Sony PRS-650. It has PDF support, but doesn't handle RPG PDFs well, I'm assuming because of the extra content rather than being a straight image. Something like Dogs in the Vineyard wouldn't cause any problems, and A Dirty World works OK, but most PDFs I tried were impossible to progress through or caused a complete freeze that necessitated a hard reset.
Whether a PDF will work I think is entirely a matter of luck for any e-Reader at this point, as they were really designed with reflowable text in mind. The AD&D 2e products that were released as RTF (Core Rules 2.0, Legends & Lore, Savage Coast and a few others) work very well on the Sony.
I'd also expect that the d20 SRD, Donjon, YAGS and a few other systems could easily enough be converted to an e-Reader compatible reflowable text format.
Reviews I've read of the Kindle DX Graphite suggest it would be much better. This one demonstrates it quite well. The larger screen size and greater resolution goes a long way to handling PDFs properly.
I've used both the Kobo Reader and the Sony PRS505. For books that use the 8.5"x11" size, the smaller screen is harder to read. The Kobo is nicer in that you can zoom in by quadrant, but you have to scroll around to see the whole page. The Sony PRS505 does textual reflow, but some RPG books are designed so that the text is not in order when the reflow happens. Also, both are black-and-white only, so you can lose some of the flavor of the text if it's colorized.
Also I've found I can get through a RPG book quicker in physical form than with an eReader device.
Your best bet would be to check out some tablets (iPad, Android, etc.), and see if those meet your needs. I think the quicker screen refresh, and larger screen size would be a boon for you.
Hope this helps!
I have a Kindle DX, and love it dearly, but so far it has been of very limited use for RPG books -- so this is a "what doesn't work" answer, rather than what does, because a few others have said that a DX "might be good" but haven't tried it. To summarize the problems:
I borrowed a friend's iPad 1 for about ten minutes, and it seemed much better for this job, although it is also worth noting that some RPG books do not render properly in Apple's PDF viewer (both on OS X and iOS), and are missing lines or words. This is fairly rare, and mostly happens (in my experience) with RPG PDF books of ... questionable provenance.
I've a Sony PRS600. For smaller PDF's (6x9 or smaller), it's great. above that, the text often is a bit small... but it's not unusable even then.
The ability to zoom in visually, in addition to the reflow option, makes reference of larger texts doable. The search feature is particularly useful. The highlighting and write-on feature makes it possible to make margin notes, etc.
The touch interface is also very natural to use, the screen refresh is fairly snappy except on certain badly put together PDFs. When the PDF page has a bunch of overlapping images instead of a one or two larger ones, it slows down. When it uses too many embedded fonts, it slows down.
The other issue is certain "recent" PDFs... using one of the Acrobat 8+ encoding/encryption formats... don't render at all.
The device is also fairly rugged. Metal case, shock resistance is decent (knocks off a table result in no damage; this is unlike gen 1 kindles). The 600 has a rubberized back; this makes it easy to hang on to, even with sweaty hands. And I'm getting 3-4 days of heavy use between charges. Or light reading over 10-12 days for a few hundred pages.
I've read the entire Vorkosigan series by Bujold on one charge, and got through the Flight Engineer series as well, before running out of power on a marathon read.
It also renders .gif, .jpeg, and .png nicely, but you're better off putting them inside PDFs, so you can zoom.
It also plays mp3 and AAC non-DRM files through a headphone port; iPod speakers work well.
Plus 3 ways to load: cable to computer, SD card, Sony Memory Stick Duo. And memory cards inserted, as well as internal memory, load as USB drives on XP, OS X, and some linux boxes; it should work with 98se or later, and MacOS 7.5-9. The desktop-side software is not needed to load non-DRM materials.
The Daily Edition (which I don't have) adds AT&T and 802.11B/G connectivity, a larger screen, and a web browser.
And the whole line is just getting updated.
I have a Kindle 1 and it of limited value for roleplaying PDFs and ebooks. I tried mightily and it not quite there yet although it main source for reading regular books.
The Kindle 2 both small version and DX works much better just a hair on the not quite there side. The main issue is flipping through pages.
I played with the iPad and was able to view and manipulate several of my PDFs and technology wise it is great. An added benefit I was able to use the photo app to view maps including some large jpgs with ease. During my limited time with it the best app for manipulating multiple files turned out to be safari! However I am sure those who have iPads will have more detailed comments.
The big problem with the iPad is that you are going to pay a premimum, the low-end version is in short supply, and limited battery life compared to the kindle.
I think we are still two or three years away from the definitive electronic device for gaming books. But getting damn close.