If you're daily driving any distance, you'll want something that errs on the side of quiet (but still louder than stock) with no droning. The HKS would be a good choice in that regard because it's dead quiet at neutral throttle and when cruising on the highway but it'll scream nicely when at wide open throttle. I found the FI cat-back to be too loud honestly but it's a personal choice.
The other consideration is rasp. Some combinations of testpipes/high flow cats and certain exhausts produce rasp which many think sounds "cheap" but it's definitely not as pleasant-sounding as a smooth, deep exhaust note that sounds like ripping silk towards redline.
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'13 Audi RS5 Misano w/mods-The Red Mist
'13 G37 IPL-SOLD
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