I'm a fan of AMD, because for the price they sell at, they run really well and I've never had any problems with them.
Although when you're buying a CPU you need to look at a two things that are important.
Clock speed (Higher is better)
Cache size (Higher is better)
Generally you should be buying a quad core at least too, as they are becoming a standard now for general PC usage. Buying anything less would be silly, but if you're going to buy a quad make sure it's decent. You can get worse quads than duals and singles, so watch out for that, just because it's a quad doesn't mean it's awesome.
You should also consider if you have enough watts to cover the CPU, and if it'll actually fit in your motherboard of course