There are a lot of great options out there..

If I were to go for the best overall cooling, and it would fit my mobo/chipset without interference issues, I'd get the IFX-14.

If I needed something a bit simpler with fantastic cooling, I'd go with the Thermalright Ultra-120 Extreme or HR-01 Plus.

However, I'm currently using the best cooling for the noise heatsink that won't break the bank, is widely available, and due to fins spaced further apart, excellent cooling on lower-rpm fans: The Scythe Ninja. It's good enough to cool a Q6600 oc'd at 3.2GHz or an E6600 at 3.4GHz without issues and keep the noise down, so that's what I have.