The disclaimers on motherboard's indicate that the HT link speed would downgrade to HT1.0 speeds. The good thing is that HT link speed does not impact the performance of the processor. As HT is used by peripherals and is separate from the link between ram-processor.
If short, buy whichever suits your budget and whichever is faster.
Actually the answer is to buy what your motherboard will support. It won't handle AM3, thats 90% certain. It might handle an AM2+, but check the manufacturers website to make sure. You'll probably need to upgrade the bios as well. (and you'll need a CPU in there to do that.)