Do you already have a DAW on your computer? Do you already have some decent plugins? If so, get the UA-25; if not, get the M-Box 2. Both are functionally the same; the M-Box 2 seems to be more expensive simply because of the bundled software.
One thing worth knowing: Pro Tools, at least the LE version which is bundled with the M-Box 2, is only compatible with some types of plugins and not with others. It mainly supports RTAS plugins; VSTs (the most popular plugin format) can only be used in Pro Tools with software that acts as a mediator between the VST format and the RTAS format (in other words, you load this other software as an RTAS plugin; the other software loads your VST plugins and translates between Pro Tools and the VST plugin). There's some overhead involved in doing that, and the software may or may not be free.
That's not to say that Pro Tools is bad; if you don't already have a DAW and plugins and you don't have money to buy that on top of an audio interface, this is a good deal; if you already have a lot of plugins that don't come in RTAS format (many come in both) or you're already used to using a different DAW and don't want to switch, Pro Tools won't do much for you.