XP was the the best, hence why it's still being supported (for a few more months). But yeah, Vista was an awful OS which is why they rushed out 7 so quickly and why they look so similar. It's just Vista fixed. To an everyday user it would appear there were no problems though.
And don't even get me started on 8. It makes a great mobile OS, but running it on my desktop? Would you run iOS on your desktop?
There is a reason that much of corporate America still uses XP, skipped Vista and went to 7 and is refusing to switch to 8.
But GNU is really where it's at.