mac is a little quieter at idle and normal driving but still is very agressive at wot. thats what i have and love it. however, people will say quality is not as great as others since its not stainless...unless you buy the SS version which is a good chunk of $$$.
the flowmaster 3-chambers, i believe they are "50 series" I have them and love them, much more mellow sounding at part throttle and idle than the 40 series.
I think louder is better, but then again I love loud cars. I have herd many magnaflows systems and they sound alot more mellow then my 40 serious flowmasters
I have Flowmaster 50 series mufflers on my car. They're dumped. With tailpipes, the 50 series Flows are pretty mellow; dumped, they sound VERY aggressive and are pretty loud.
I had dumped 40s before, but the sound level was ridiculous.
Dynomax exhaust is also something to consider. A friend of mine has it on his foxbody, you can't really even tell it has aftermarket exhaust at idle, but it's not a smooth, mellow roar at half or WOT.
I have some jegs mufflers from their catback kit I bought. They might be quieter. You can have them both for $30. I bought dynomax turbos for a lot quieter sound.