Ouch.... PSN ain't THAT bad... well maybe it has CF, more people new to the game series, and rambunctious assholes... ok I HAD A POINT BEFORE OK!? But still we're not ultra terrible.
I don't see the need of getting an Xbox just for this game, I mean sure you get to meet more of the community and get away from how terrible PSN is but ehh, I find it to be a waste of $120 + XBL membership.
What Force said. And you'll more than likely bore more quickly playing DOA on the 360 version though since there's not many people playing. You'll see a lot of the same folks repeatedly. Just don't get your hopes up.