I'll come here to end this:

Based on personal experience with both games (don't actually own either, but I've played them both online/offline extensively), I'd have to say that, hands-down, Metroid Hunters is the better game. It's simply more fun than Socom. Neither game appeals to me all that much, but I'd definitely give the edge to MP:H. Better VoIP really isn't an issue, as it sounds just as good on the DS (which is really saying something, due to the "lower-spec" nature of the DS against PSP). I prefer Metroid's controls anyway.

Hunters ftw!