Go Perrin or MRT. The HKS is really good if you're on a tight budget, but the aforementioned parts do a much better job of dealing with the wastegate exhaust. TurboXS(if memory serves) makes a funky looking, two-piece DP that Mastro threw on a customer car a couple of weeks ago. It made me think of a whale when I saw it, but it seemed to be pretty well put together.

Whatever you do, get something that allows the wastegate to exhale freely and make sure it's stainless, for obvious reasons.