I think XP was great in its heyday back when it was considered much better than Vista, and SP3 was still new. Time hasn't been kind to it however, with all its gaping security flaws due to a NetScape-era approach to the Internet and an antiquated visual design that has NOT aged well.
Like soupcan, I also never had a problem with Vista for the 3 or so years I used it. I don't know what exactly the big fuss everyone always has over it is about.