Whoever makes that Athalon better watch out, it's awfully similar to AMD's Athlon name.
Anyway, both processors will win certain benchmarks and loose certain others, while Intel's XEON processors (which also have 64bit versions) will win some others. You have to decide what you plan to do with your computing, and then from that you can figure which processor performs the best at that task and that one will be "the fastest" for you.