beviet almost every post about HSF on this forum seems to recommend the Thermalright SLK-800. I have the A-X7 and am very please with it but if I had to buy one now, I would choose the SLK-800 because people are getting better cooling results. The SLK-800 is only $38 at NewEgg and the other two you mentioned run $28 and $33 respectively. It would be worth spending the extra $10 for the best considering you only have to buy it once.
Sorry just found out the SLK-800 is available at SVC for only $29.99