I have some really quiet FlowPro 20 true duals... changing them out for Magnaflows.
I've been reading and researching alot over the last few days. Spent about 2 hours in 3 shops talking shit with the owners and a few hours listeing to clips on youtube. What I've learned is that exhaust is so much a personal thing of preference man. If you want to go with a raspy or rumbly sound no matter how hard you hit the gas, go with Flowmasters. The downside of Flowmasters is their chambered design allows for two things: less flow due to their chamber design, and possible droning due to their spot welded design.
If you want something less quiet with more flow, go for some Magnaflow straight through designed mufflers. They are loud when you get on em though....and I think the larger the size of the canister, the quieter the sound.
Just thought I'd chime in my .02
BOSS