Dynomax Ultraflow. From personal experience I will tell you the Ultras sound very good at idle/low RPM but not too loud but will absolutely scream if you floor it. Even with an OR pipe they aren't too loud at all.
2000 Mustang GT Steeda #0048 34k miles. 99 Cobra 4V swapped, FTBR IRS swapped, exhaust, tuned by James Gordon.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.