To get close to apples and apples, you need to add in a PC-Programming method for the MX-500, which means either the MX-500PKG (which includes the URC-8811 and a JP1-Cable) or the IRClonePKG (which includes the IRClone-MX device). Pricewise, both are pretty close to the SST-659's street price so it's still a fair fight.
Given those options, I'd probably opt for the MX-500 / IRClone setup. You get all of the advantages of the MX-500 with the ability to program the remote using your PC. The SST-659 is a great remote as well, and has the built-in TV listings if you're interested in that (though I find it useless if you have a PVR like TiVo).
Check out the physical aspects of both remotes online, and see if one appeals to you more than the other. Then check out the software for both (
Harmony /
IRClone) and see if you prefer one over the other.
In short - you won't go wrong with either choice. They both terrific and popular remotes that will control your entire system. The details will decide for you. It's personal preference!
David
www.BlueDo.com