At home I have WinXP (home edition) and W2k The XP is set to classic and really I find little difference. But then, I'm not doing anything fancy.
I've also got both at work (Pro editions) and NT servers. All of them seem pretty well bug-free now.
It's your choice, really. The only difference is that eventually MS will stop supporting W2k before XP. But then, there will no doubt be another version...
How can they keep improving?