I haven't listened to as many amps as most of you guys, but I can pretty truthfully say that I haven't heard much difference from one to another. But then, I haven't listened to them A/B nor through very high dollar speakers which might demonstrate differences better. I Have heard massive differences from one speaker to another, however. The difference between a couple of decent amps is nothing compared to the differences between speakers!
I guess that is one of the reasons I get so bent out of shape reading reviews describing all the differences between speaker cables. I think that if you can actually hear a difference between two cables, then at least one of them is defective. (This assumes that they are of adequate size to carry the load.)
In my opinion, for those of us building a system on limited budgets, most of our money should go into the speakers.
(This applies to home sound, not professional stage reproduction, about which I know nothing.)