I'm currently running an X2, pentium-m, 2 pentium 4's, and a pentium D. In order from favorite to least favorite:
1. AMD X2 4200+ @2.618ghz
2. Pentium-M Dothan 1.6ghz @2.4ghz
3. 3.2Ghz ES P4 @ 3.45ghz
4. unknown P4 ES @ 3.38ghz can probably do higher once water cooled.
5. Pentium-D 830 @stock speeds, cause it runs like a flame thrower and doesn't OC at all.