The computer I usually use runs on XP but our laptop is Windows 7. 7 is better for the more causal users but if you use a lot of different programs and applications, you should stick with XP because 7 won't run them all.
Vista on my laptop, 7 on my netbook. 7 seems to be pretty good (much better than Vista) but it's a lot different from Vista/XP so it's taking some getting used to.
I own 2 computers so...
XP for my netbook (netbook = mini laptop)
Older one/Vista for my used computer, which is downstairs. Ahh, living in a house that is possibly a mansion.
I got a Mac but my Dad uses Vista on his computer (computer I used to use) and my sister got a new computer about a year ago that runs on Windows 7. 7 looks pretty cool.