phoenix gold...no contest...phoenix gold is not the best but definately respectable...hifonics are for if you need lots of power and are on a tight budget.
Also note that Hifonics rates their amps higher than the actual output. Someone posted in another thread that their 1500D actually puts out about 1000w RMS and that may be a generous rating. I recently heard one of their "Zeus" series amps running at 2 ohms into a pair of 12s. It was supposedly 600w at 2 ohms. Uh, not hardly.
There are lots of good mono amps on eBay in your $400 price range. Do some searching on eBay, then do some research on a few of these car audio forums.
Kicker KX1200.1 - $400 or less. Alpine 1200D - $370 or less. Memphis Audio PRD1000.1 - $310 or less. Diamond Audio D6 1000.1 - $Approx. $400. JBL1201.1 - $350 or less.