Best sounding mufflers for 05 GT?

Yep, the Flows are high. Look into the Pypes Violators, they sound pretty good. I'm thinking about the MAC axle back kit, too. I like the way it sounds, plus I'm always looking for something just a little different. I had Flows on my '99GT, but I'm looking for something different this time around. Also - don't expect any gains from the muffler swap. The stock system on these cars flows very well from the factory, so it's just a change in sound that you'll get. The stock system does leave a little to be desired in the sound department.

If you go with an O/R h or x, you'll have to get a tune. You can't do much of anything to these girls without a tune. It's a good first mod, for sure.

X will generally give a few more HP than an H, but they have more of a "raspy" sound than a traditional H. I personally like the sound of an H pipe more, but there seem to be more options in an X over an H for some reason. Hit up Youtube for some sound clips and see what you like. American Muscle also has several sound clips that compare stock to aftermarket.