for the long run id prob go with a perf muffler...glasspacks are pretty much disposable..i bolted one right on the exhaust manifold of my '56 mercedes that im restoring, and it didnt last very long...
i have a 40 series flowmaster on a 2.5" pipe, cut out all of the old exhaust pieces (from cat back) i didnt notice any drop in torque, but i did notice the car hauls a little quicker once it passes 40 MPH (according to the buttdyno) it will cost a little more than a glasspack to install, (i paid 80 total, but it could be more cause i knew people and they let me use their muffler shop's tools) expect to pay anywhere from 150-200, cost of muffler, labor, parts,...etc.
sounds cool, kinda loud, it does not resemble a civic or import sound, more or less sounds like a camaro...i like it. go with the muffler for longevity...
my 40 series is single in-single out, an 80 series woudl give you single in / dual out...check out thrasher's setup, he's got an 80 series...look at my pics of the rear of my car, yuo can see what it looks like installed...