I'm not big on either UI, though I'd give the xbox the edge until ps4 gets folders. As far as the UI being the deciding factor for which system I buy my games on, fuck no. If I have to choose between a slightly speedier UI or better fidelity and a bigger multiplayer user base, I'll pick the shit that actually affects my gaming experience. The seconds it takes to get to the game from the UI are miniscule compared to the hours I spend in the game. I think it's fucking insane to choose to play a multiplat on the xbox with the UI as the only reason if it's got worse performance (read: if your friends are on there or you're a trophy whore, those are perfectly acceptable reasons to do that, though. D3 would also be fine as the two versions are essentially identical). That's just my opinion.
Also, any benefit of the speedy voice ccontrols is decimated by the 20+ minute wait time for Disc based games to install. Shit is horrid, as are the patch sizes of many games.
Xbox is my main media box, though. I love being able to switch from Guacamelee to TV to Netflix instantly. And suspend/resume is the best.