"Best" is a relative expression, it depends on how you look at it. For some, best is the sheer amount of performance it can deliver, and for others it's the performance vs. cost. It's sort of a see-saw situation, and for most DIY folks, AMD is a better solution than the Intels, which can cost far more for only a marginal difference in performance. Most of the time, an AMD/ATI solution is cheaper than an Intel/nVidia solution (there are some exceptions of course). An example- AMD Phenom II X4 965 Black Edition Clock: 3.4 GHz Cores: 4 L2 Cache: 4 x 512KB L3 Cache: 6MB HT: 4000MHz Die: 45nm Thermal: 125W Price: $195.00 Intel Core 2 Quad Q9650 Clock: 3.0GHz Cores: 4 L2 Cache: 12MB Bus: 1333MHz Die: 45nm Thermal: 95W Price: $330.00 As you can see, not too much difference in the specs, although the benchmarks do put the Intel ahead of the AMD by around 5-20% depending on type of benchmark. If I were trying to save some money (who isn't?) I would go for the AMD. However if money was not an obstacle, I would go with the Intel. A 70% price increase for the Intel is a bit much to swallow for anyone on a budget.
Intel has been the best for the longest, but their was no competition for years until AMD showed up with their cheap cpu's and comparable specs. Depending on your budget and what you are wanting to do with the pc in the end will determine what one you will choose. Kinda like buying a car.