Check out Dans Data site on the Web. It's about the most complete comparison out there. Even better is that he's also about the most impartial reviewer. Heatsinks are performance, versus preference, versus size/fitment, items to many people, and the "best", may mean different things to defferent people.
That being said, Take a look at the big Alphas, as they are near the top, performance wise, and if you want to use ducted cooling to the outside, then they ARE the top, as they are designed to run in reverse flow mode, provided there is no heat source close to the heat sink. Drawbacks? It's very large, and requires it to be bolted to the board, making quick changes a memory. Ths Swiftec are also top notch, and offer more models to choose from to fit your needs.