What qualities do you look for in a good amp?

I would first have to know what speakers they are to be mated with if I was going to aim for the best synergy.

I would then research what others have found to be the best match with the speakers I will be using.

I would then go and try to get an audition of the amp.

Lack of grain
Soundstaging
Detail
Bass

Those are all points I would listen for to see weather I like the presentation before purchasing.

Good luck!