Phenom II X3 > Phenom X3 > Athlon X2
When in doubt, go for more cores over clock speed. Unless you're using a single threaded application very frequently that won't suitably run on one weaker core and has no potential to be updated to be multi-threaded. Most apps are multi-threaded these days, and only more are going to show up. I wouldn't go for a dual-core build these days unless its a very budget, surfing/music type machine.