3.5e or Pathfinder
5e is new, 4e requires knowledge of game concepts from other dnd games and combat takes ages, and ADND/2e/clones are very rough on new players. My greatest strike rate with introducing DnD to new players/roleplayers who haven't played it is 3.5e. I include Pathfinder as the two games are very similar, with some people calling Pathfinder 3.75e. I personally prefer 3.5e, but the difference is slight.
I only have limited experience with it, but I feel again that it relies on a certain amount of dnd 'meta knowledge' to run quickly and easily. If you are a new GM, or if your players don't have experience with DnD, I feel a different edition may be easier to understand and use.
It obviously depends largely on your group and what they like to do, whether that's crunch minutiae, tactical miniatures combat, 'die for no reason a lot', etc. My suggestion would be to run a couple of games in one, and if they are not liking it, switch out for another.
My personal largest strike rate has been with 3.5e/pathfinder, though, so that's what i'll recommend you start with.
Books - 3.5e
There was a re-release of some 3.5e books, if you're looking at playing 3.5e I would recommend picking up the core set - the Player's Handbook, Dungeon Master's Guide, and Monster Manual. All are quality products. For interesting material that will add to any 3.5e game, I can recommend the Expanded Psionics Handbook, Complete Warrior, Complete Arcane, Player's Handbook II. A monster manual or two can be handy if you're drawing a blank on what exactly is infesting the basement of the House of Twin Spires. It's worth noting, although I explicitly cannot encourage you to pursue this or give you any advice on doing so, that there do exist pirated copies of 3.5e books in pdf form.
There's a Beginner's Box for pathfinder, which I have not personally used. My experience of these 'boxes', though, is that they are geared to absolute newbies and generally not as fun as simply buying the actual rulebook, even for absolute newbies. If your group has rpg experience, the lack of choice I assume to be present will probably annoy them, and you're probably better off picking up a copy of the Pathfinder Core Rulebook.
Additionally I hear good things about the Advanced Players Guide and Ultimate Combat, and you will need their version of a monster manual, the Bestiary.
Interestingly for Pathfinder there are several 'Adventure Paths', campaigns in a book designed for you. Of those, i've read through Kingmaker, Carrion Crown, and Shattered City - I can recommend all three as easy to run and hopefully interesting.