Let me know your guys opinions

Well the HDS312 is a great woofer and will take more power than it says. They both have a 3" Voice Coil but the HDS312 can handle more power, probably due to better cooling and/or more coil winding (thickness.). The SoundQubed woofer has nearly TWICE the XMAS which means nearly double the excursion (more air movement.) The Rockford T0 has better low end capability though while the HDS312 is more tuned for mids/highs (this is really good for overall SQ and bass.)

So personally... I'd get the SoundQubed all day everyday. More power, More Excursion, Better SQ.
You're also comparing two completely different prices woofers... You could get almost 2 HDS312's for the cost of a single RF T0. You could get a SoundQubed HDC3 that will rival both woofers for less than the cost of an RF T0.

I've owned both subs. If i absolutely had to choose between the two i guess i would go soundqubed. That being said. For the money I'd go a whole different route.