loudmouth is good for a stock car. if your going to add longtube headers and an offroad y-pipe than stay away from it. though it also depends if you like that sound, some people do some people dont, its personal preference. if you search about it youll find that almost everyone has complained about the rasp and drone. some have solved it by switching the mufflers to either a dynomax bullit or a borla xr1 which helps, plus if your running cats it will take care of some of the rasp. gmmg makes a great sounding exhaust and as 99% of this board would agree, its one of the best (esp with lt's). the downside is the price of $700 or $850 with the oval tips, but also consider that you pay for the quality you get, and its definitly worth the money. TSP has come out with their line of true duals with 18'' bullit mufflers dumped before the axle which everyone has seemed to love as well, but you would want lt's before you would buy the setup, but the sound is unbelievable. other popular choices are hooker and magnaflow catbacks. loud is only defined by personal prefence, your going to get a whole bunch of different opinions, (ie: if i owned a hooker catback i would say go with that, same with gmmg, lm and every other system) so the best way is to listen to as many as you can in person. go to
www.ls1sounds.com and you should be able to find what you lookin for, also remember to appreciate the exhaust sounds more, you should listen to as many as you can in person. also use the search, theirs tons of info floating around this board by people who have been in the same situation you are in (i was one of them also).