Got my self a copy of both NBA Live 07 and NBA 2k7 so heres a review for both of them.
(Note I have them both on PS2, so the reviews are for PS2.)
NBA 2k7:
The graphics for these games are pretty much the same as NBA 2k6, but the players clothes move just a little bit in 2k7. The look is still better than Live 07 however. The new introduced signature shots is a great idea and it's a massive ad on to the game. Only problem with that is that if you want to edit a player and have them get signature shots, you can't. So after all the players with signature shots retire, everyone will have same shots in the game.
Passing has also improved in the game, with more realistic passes. When in bounding the ball it won't be that easy as the AI in the game has improved dramatically. A lot more turnovers are in the game. If you play on Hall of Fame difficulty, you will get one hell of a challenge from every team.
Also a few new camera angles have been added to the game, which also makes it more realistic.
NBA Live 07:
Let me tell you something about this game, the game play is awesome, the graphics, are horrible!! There are only 4 camera angles in this game, and 3 of them are crap! Baseline low, baseline mid, baseline high, and press box are the camera angles. If you aren't used to a side angle like press box, like me, you will have a hard time in this game. The other 3 angles are crap and either you are too close and can't see all the players, or you are too far and can't exactly see whats happening. Seriously if this game got better camera angles, and kept the graphics the same, then this game would sell way more copies than NBA 2k7.
This game also has the freestyle superstar, which is a great addition. Richard Hamilton got his nasty jump shot, and Vince carter will dunk on anybody. This games goes in detailed with every single player, which is really good.
Both are still great games, and if I was you, I would buy a copy of both if not already.