This is the question that has been on everyone's mind for quite a while, and an issue I even looked at more than 4 months ago. I compared Oden to Alonzo Mourning and Durant to Dirk Nowitzki, but neither of those accurately sums up these guys' games.
With Kevin Durant, you have one of the most versatile offensive weapons ever to come into the NBA. That's not even exaggerating. He has a great touch from the outside, and with his height can get the ball off against almost any defense. He also has a quick first step and can get to the basket and finish. If that's not enough, he's also got a developing postup game in case you try to guard him with someone smaller.
But he's got a lot more to his game than just his scoring ability. He's unselfish with the ball. He's got great instincts and solid athleticism, which allowed to be in the top 5 in rebounds per game as a freshman. He also has long arms, which can make him a defensive force as that part of his game matures. He is a complete player, and can do things offensively we haven't seen before in one player.
Oden is the opposite. His defensive game is farther along than his offensive game, and his offensive ceiling is probably a little lower. But defensively he shines. I think that once he gets drafted he will immediately become one of the top 5 defensive centers in the NBA. He is extremely athletic, quick, and has great shotblocking instincts. I really think he compares to a Bill Russell or Dikembe Mutombo as far as his defensive ability.
Offensively, he is definitely coming along, as we saw in the title game against Florida. It's very clear he wasn't at 100% all year long, and has been mentioned, I think this will help in the long run. He has become very adept with the left hand and showed he can finish with the right as well. He is raw on the post, but showed the quickness and athleticism that makes me think he can be an elite offensive center as well.
There is no doubt that these are both special players... barring injury, I can't see either of them disappointing or being busts. In my mind, Oden will be a 20-25 PPG scorer and one of the best defensive centers ever. I think Durant will be a 25-30 PPG scorer and eventually be a very good defensive player as well. If I had the choice, I still think I would take Greg Oden, because I think his defense just makes him a little more valuable.
But who would you take?