If it's between TTT and T4, I'd say get Tekken 4. Less characters and a tiny bit slower dinamic than TTT, BUT, superior graphics, continuation of storyline (in an awsome way, specially for a video game) and well, overall, just cooler IMO. My suggestion would be to rent both and check them out for yourself before buying them.
As for DOA2...
This game is only 30 dollars brand new at EB. If you don't mind seeing a lot of "FEMALE JIGGLING"
you will like this game.
I own both T4 and DOA2 for PS2 and I enjoy them almost equally. DOA2's graphics and gameplay are just awsome, the storyline is not so bad (although it ain't close to be as good as T4's) and it's an alternative as a fighting game, is not the same as most of them, you'll know if you play it yourself.
I would say, after all, get Tekken 4, but not without playing the other 2 games before. Although IMO T4 and DOA2 are both superior to TTT.