Data Sprites appear to be worse than other sprites in almost every way at a reasonable level of resonance. In particular the Courier sprite has access to most of the same abilities, gets an extra complex form, gets a few more stat points in every stat, and gets the Hash power (which is similar to the Data sprite's Stenography ability but, rather than requiring an incredibly low static DC to defeat, always works without fail). Is there something I'm failing to notice about the Watermark power? Is there an errata I haven't read that buffs data sprites? The ability to use linguasofts as CFs rather than the normal way? What's going on here?
First off, Data Sprites have seemingly exclusive rights to the Sniffer and Stealth CFs as far as Sprites go. They use this to get to data undetected. Couriers have no such safeguard. Their whole point is to keep data that they are assigned to safe while in their care, burning it if they can't protect it. Data Sprites get in and out undetected, and can find files that you don't already have the information to find. It's like saying "Why send a spy when I can send a knight?".
The Stenography power is about hiding the data from use, where Hash is essentially keeping a guard on the file. If the Sprite is defeated or somehow chased off, the already normally detectable file becomes unencrypted. So yes, the Courier may have higher stats but it needs those to fend off would-be attackers or you lose the file forever, where stenography doesn't change the integrity of the file and in fact, you can use the two abilities together.
The Watermark power is more one of reconnaissance and roleplay than of direct mechanical use. The watermark can be used as a message that nobody is looking for, or better yet a message to anyone. I immediately think of the old (let's call it) workaround for calling collect. When the service placing a collect call would ask for a caller name, the caller would very commonly leave a very brief message for free and the receiver would deny the call and therefore the call charges. A watermark can also be used like trail signs. When perusing a system, and you come across a file with a watermark of "Don't open: Data Bomb - newbieWanKinobi" you avoid it.
Or, better yet if you're a consulting Runner, once you find an object file you can leave a marker for the actual hacker without accessing the file and disrupting any defense in place. Keep in mind that Data Sprites have access to the Stealth, so they can in fact "paint a target" so to speak. So your Data Sprite gets in there, finds the target file, and you send in your otherwise lost Crack Sprite to get what you need. Or a more malicious (and probably desperate) mind could use a Courier Sprite to Hash the target, destroy itself, and ruin the file forever.
From a computing standpoint, hashing is a way of organizing the data such that you need a specific legend or table to make heads or tails of. "Stenography" is like renaming a file on your desktop from "Email Password.txt" to "Cheezburger.jpg" and nesting it in the folder "cat pics" in the folder "web humor".