I've tested both the AC Freezer 64 Pro and the Xigmatek HDT-S1283. Unfortunately, I can only give you an incomplete picture of both HSFs.
Though there are many who swear by the Arctic Cooling Freezer 64 Pro, I didn't find it to be particularly impressive when used on a S939 dual-core. It worked fine on a single-core A64 3700+ San Diego, but single-core CPUs put out considerably less thermal energy. As I said, though, there are many reports of this HSF being good even for dual-core CPUs; there are even some who say it's fine for quads (!).
As thlnk3r said, lapping and modifying it will improve performance. However, I sold mine to a client before I could either lap it or modify it with a better, stronger fan.
The Xigmatek HDT-S1283 is a current budget-friendly favorite these days. I'm testing one at the moment, but am having difficulty matching other peoples' reports of excellent temperatures. I believe part of my difficulty is from two things: 1) The mounting clip mechanism (for S939 application) simply does not generate nearly enough pressure to be effective, and 2) I've yet to find the optimum way of applying TIM (thermal interface compound) to the heatpipes.
As an aside, I find that HSFs which rely on mounting clips instead of a bolt-down attachment mechanism, like these two, aren't as effective as bolt-down CPU coolers. I favor a high-pressure mounting mechanism.
Hope this helps you make an enlightened decision!