As you go up the food chain, the preamps get higher quality, the gain is usually higher (some mics need higher gain).
Here's a link to a comparison chart:
The Audiobox 96 and Studio 26 are both the most recent generation. (Less than 4 months old as of this post.)
Every generation tends to be an upgrade from the previous.
I own two 22VSL interfaces and they are rock solid. The Studio 26 is my current fav, with higher gain and cleaner preamps.
Not that most people can hear the difference, but if you can swing it, the Studio 26 is a step up from the iTwo and Audiobox 96.
The chart provides some additional details.