I'm getting an MPC3000, but I'm sold on the MPC2500, too. Much better build quality than the 1K and the 2KXL.
Decide what features you'd want, what sound you want, and get the one that matches your criteria.
If you don't need time stretch, then the MPC60, MPC3000, or MPC2K might be good choices. (If you do, the MPC2KXL, MPC1000, MPC2500, and MPC4000 are the ones)
Is build quality important to you? If so, the MPC60, MPC3K, MPC2500, and MPC4000 are the ones.
How much are you willing to spend? Do you want it new or used?
Go look around on ebay and some other webstores to get an idea of the usual price range.