Honestly, I've been thinking about this for a while now.
Logic says that with all the new features they had in FFNY, it would easily beat Def Jam Vendetta.
I had more fun with Vendetta, though I'm not sure why.
Maybe it was a combination of the intial novelty of rappers beating the crap out of each other with the fact that it had a submission based combat system that should have been in WWE All Stars.
I felt like you could do around the same amount of moves in both, even though there was more variety in the second.
I would like an HD re-release of both on PSN, I would definitely get them.
My vote is Fight For NY, but that is mainly due to the expanded customization and fighting styles. I'd alternate between both though, because Vendetta had better original characters in my opinion, even if they were downright cartoony.
DAN G 4 EVA!