when it comes to thermalright vs. swiftech, i've noticed very little difference in performance. the only real difference you will notice will probably be in your choice of fan. let's say a tmd 70mm versus a vantec tornado.
i've also had to make the decision between a swiftech and the slk900u, i chose the slk900u for ease of use and installation, and the fact that it fits both platforms. it is especially easy to put on a p4 system. just two snaps and your done.