It really depends on what you're looking for. You ask "Which one sounds better?". What kind of a sound are you looking for?
I had a 40 series with single 3" exhaust on my '92 Camaro, and it sounded great! A very loud rumble .... you could hear me coming a mile away.
On my blazer, I wanted a relatively quiet exhaust. Something that wouldn't attract attention, be comfortable for long hauls, but still give low RPM performance. I went with the 3 chamber 50 series SUV flowmaster and a dynomax high flow cat. It is exactly what I was looking for.
If you are looking for loud, try a single or dual chamber flowmaster. If you're looking for quiet, I would suggest the 3 chamber 50 series SUV muffler.
Thomas.