Best amplifier for sound quality for subwoofer(s)?

Lots of good choices, but some of those brands are super-expensive. Whatever you go with my 2 cents would be to make sure the amp is AB and has a 24db crossover...to me the 24db crossover has a HUGE impact on the smoothness, musicality, depth and overall enjoyability of the bass. I have a Polk Momo amp that I love, but I believe the quality of their amps have come down quite a bit in the last couple of years.