Well, I've played the PS3 demos for the two big baseball games, and MLB The Show is lightyears ahead of the latest 2k game. Here's a quick breakdown:
Graphics: The Show is stunning, with crisp player and environmental details, right down to a complicated reflection of the stadium seen in the players' helmets. Player movements are about as realistic as I've seen in a baseball game. MLB 2k8, on the other hand, looks like a Sega Genesis game. Graphics are ridiculously choppy, and not nearly as clean as The Show. Awful camera angles for gameplay and replays also.
Gameplay: 2K is continuing their attempt to make a near-buttonless experience, letting you control pitching, batting, throwing, and probably other stuff with the right joystick. Does it work? Well, if you like Skate, then you might go for it, but otherwise, I'll stick to The Show's classic button interface. The Show can get a little frustrating in the fielding area, and baserunning could be a little better, but it's manageable. 2K doesn't do itself any favors by having the CPU hit a homerun everytime you fail to understand their ridiculous pitching system.
Audio: 2K features Jon Miller and
Joe Morgan, who I happen to think are really annoying. I'm not sure who The Show's announcers are, but they interact very impressively with the gameplay and replays, saying things like "It looks like they called that one wrong, wait, stop the tape here (Replay freezes). No, they got it right!" Music is better too, featuring classic stadium tunes, instead of annoying pop tie-ins that 2k boasts, such as Modest Mouse (Modest Mouse was so much better when they were a bunch of drunk rapists).
Realism: Part of The Show's great appeal is its phenomenal attention to detail. For instance, when a runner has a close play at first, he will make the "safe" sign as he slows down, and then react when he sees the umpire's call of "out." The realism almost goes too far, as the umpires are annoyingly prone to making questionable calls of ball and strikes. 2K's realism? Mmmm...Did you think Super Bases Loaded III was realistic?
Overall: I'm surprised that 2k is even releasing a demo to go up against The Show's truly impressive demo. Maybe if EA's bid to buy them goes through they'll step it up a bit. Stick to beating up hookers, Take Two.