I'm thinking custom 4" from the turbo back, and a nice Magnaflow Ti can out back.
The trick is adding the resonator in between where the stock rear cat goes, and the bend before the rear axle. Without the resonator, most exhausts are too loud.
Burns makes some nice "bullet" type exhausts that could be adapted as resonators and so does Borla.
Too bad nobody makes a nice 80mm Ti catback with a resonator for the MK3. That would be worth spending a few bucks on, and I'd let my HKS Turbo sport catback go. (Would not mind a Ti downpipe in 80mm as well, but it should have some kind of flex section between the turbo and the lower part. Nothing worse than sending any impact force back up that long DP lever arm to your turbo housing and exhaust manifold.)