Depends what kind of frequency response you want. Buddy of mine just got the Avalance 15 ported, I believe tuned to the low-mid 30s, hits lows awesome but thats about all it does, and it doesnt need 1000rms, its on a JBL 600.1 and it hits pretty hard. But Id go for 12s if I were you, go with the nicer ones though like the M6's (which were discontinued and are now the D6's). Im a big Diamond fan though, not that ascendant is worse, but I like DA's combination of spl and sq in their subs, theyll slam and still sound amazing.

GL
Kevin