I have been enjoying the Infinity Kappa 120.9w subwoofer. The sound is tight, better sensitivity, and it costs about the same as Dayton HO.
I am sure Dayton HO12-44 sounds pretty awesome, just be aware that it has pretty low sensitivity. According to PE it's something like 83dB at 1w/1meter, which is 2-3 db lower than a typical 12 inch sub. I guess that's the cost of working well in a 1cu ft sealed box, having ~20Hz resonance frequency, and F3 of 39Hz (which is pretty good for a sealed 12). It's a very intriguing sub, just make sure you have a good amplifier. But with "only" 300-500watts, I'd probably just use the Kappa 120.9w I mentioned.