In my experience front loaded subs (now I have to generalize hear, there some high end designs that seem to beat this rule) tend to have a tighter punchier sound. Chambered subs tend to hit a little lower, but looser, and often a little louder, but you are more likely to get a rumble. This can be just fine for home theatre, many types of electronic music etc... If you are doing rock music though, it's really important (at least in my opinion) that a sub "hits" rather than "bumps". Basically, front loading seems to allow the sub to have a little more attack and immediacy, where chambering tends to add volume, dispersion, and depth. That isn't to say though that a front loaded sub won't be loud enough or throw far enough.
It's kind of like at concerts. There are a lot of people out there that really like the sound of 15's for subs instead of 18's. Often times 18's will be amazingly large. You will actually feel the room. 15's seem to be a little more contained. The room may not rumble as much, but each kick drum shot kind of hits you in the chest. It's a more immediate event whereas a larger sub often tends to just sort of surround you in it but with much less definition.
