People are more and more confused on what the better operating system is, but it's really not that simple. Most people care about performance and that applications just plain work. For XP, it is actually faster for doing common consumer and business tasks on PCs coming out of sleep mode. These tests were actually commissioned by Microsoft themselves which was kinda odd.
The performance tests showed that XP operating system remained faster than SP1 in 61 percent of operations grouped inthe consumer test suite and faster than 46 percent in the operations business group. The trials were done on identical PCs and even compared to OS X.
On most tests, XP were pretty comparable to Vista SP1. The only problem that they didn't test was that many drivers and apps don't work that well in Vista thanks to poor drivers. Overall, its an interesting test and shows that XP is still faster than Vista which wasn't much of a surprise.