I don't know about the ActiveCool, but I know that this Zalman baby is a very good cooler. It's really quiet, keeps the CPU pretty cool and very good for overclocking. Plus, it looks nice
I really would go for the Zalman. A few weeks ago I read some Dutch roundup on AMD coolers and these Zalmans were the winners. Best performance, low noiseproduction. Of course, the best one is the one made entirely of copper.