You get a better answer in these forums
http://www.operationsports.com/forums/basketball-other/
But, IMO I say keep both. Both are really good games. One does something better than the other but, it's up to you man. Check out the demo of 2k10 and how you like it. To each his own. You may not like it, you may love it, but, you won't know until you play it.