I had the Dynomax Ultra Flo Oval on my truck. It was actually the first muffler I put on it because Summit had a $50 rebate on the $70 muffler. It is a very free flowing muffler and power was great. BUT....it wasn't what I wanted. If loudness was on a scale of 1-10 with stock being 1 and flowmaster being 10, the Ultra Flo oval lands right about a 4. Very mellow, very tame muffler....but it did sound good, just wasn't what I was after. If you're after a very efficient muffler with a little bit better sound, go Ultra Flo Oval.
Sidenote: I took my flowmaster off a few months ago because I got sick of it being dumped(no tailpipes), so I put the Ultra Flo back on it(turned down this time) and boy oh boy....I couldn't even hear the darn truck running!! All I could hear was engine, not exhaust. VERY quiet compared to flowmaster.
'01 XLT disguised as a '03 Fx4 Level II.