Like Skip said, Drags goes by the size and number of subs where USACi goes by the amp rating, it's the 4 ohm rating of the amp. It's hard to make a system competitive in both formats but it can be done. Db Drags has a lot of rules, where USACi has very few. The rules defining Stock/Street are pretty close. It's all a matter of preference, but I think overall dB Drags is much better than USACi.