Disregard my pipes comment. OP wants least amount of resonance. That will pretty much eliminate Roush's and probably other straight through type muffler.
The loudest with least amount of drone usually falls back to Borla. I've heard Corsa may be an option too, but have not heard these personally so can't tell you if they drone or not. But for the price, I hope they wouldn't.
2012 Mustang GT, Ingot Silver, 6M, 3.73, Brembo.
Whipple 2.9, Flowmaster AT Cat Back 817500.