I've got 2 PC's. One running XP Pro, and the other running the 2000 that was on the XP machine previously. Both are great OS'es, but I have found that on the 2nd PC running 2000, that me (and the rest of my siblings) are wishing for the XP GUI on the 2000, and especially Fast User Switching. I prolly will end up shelling out $100 for a 2nd copy of XP Home for the 2nd PC (damn Product Activation!!!!).
I really, have not found any difference in stability or speed between the 2, and really, as far as I'm concerned, XP does nothing but build on 2000 SP2, this may be a bit biased because I (unlike most) like having the Limited Burning capabilities of XP, I like Zip Folders, I like the new Start Menu and GUI, and I love Fast User Switching and the quick boot times. Really, it's like I say. XP does nothing but build on 2000. The only 2 things I dislike about it are Product Activation and all the newbie Security settings, but you can for the most part disable all that, it's just difficult to find where you turn them off.
I think that I'd have to give the nod to XP Pro/Home. I voted for XP Home, but I will caution though that XP Pro or 2000 Pro will be prefferable in Server enviornments because Home can't log into a Windows 2000, or NT Sever.