If a non turbo, non boosted opinion counts then i will add my thoughts.
Most turbo enthusiast these days seem to say that 3" is best to avoid boost creep and allow the turbo to spool as fast as possible. As far as brand i think just about any 3" will do the job about the same but quality definitely comes into play here.
My first response for a turbo exhaust has always been ARTech, Abe makes phenomenal parts and can do a full hotside including turbo manifold, downpipe, catalytic converter or test pipe and exhaust. Since you dont already have the turbo kit but i would definitely email Abe,
abe@artechfabrication.com , about a setup because when considering a turbo setup i compared prices and his are INCREDIBLY competitive especially considering its custom and will be much easier to install since he uses all vband connections. I don't know if you have seen any of his handiwork but here is my recently completed 2.5" exhaust from him:
Pricing is in my build thread on page 14.
One really great thing about Abe is he can do whatever setup you want for just about any turbo (t25/28/30, t3, t4, etc)...log style manifold, tubular manifold, ewg (external waste gate) mount, 2.5" or 3" exhaust, test pipe or catalytic converter, resonated or non resonated, small muffler/large muffler/no muffler, single or dual outlet and probably even center outlet.