Hard to say, I still like the original P90 design, it's small and compact and changing the magazines is easy peasy, lemon squeezy.

The other one looks okay, looks like it does a little bit further in range maybe, I can't say that the ammo changer is that much easier to use, because if you're shaking, getting in that little slot can be kind of difficult, and the P90 you just slap the fucker on top and you're done.