As many have stated already, often the loss of a few horsepower may occur with true duals...but if done properly with a crossover pipe that loss is minimal at best. Also many riders do not like the "look of 2 into 1, and if you go with 2 into 1 into 2 there really is not much difference...if properly designed in all three cases.
I have no regrets, I ran straight pipes and properly tuned Stage I mods made the look, sound and performance much more than stock...your ride you decide.