Well, like I said, I think those three brands I mentioned are the best. They are all stainless steel, which most of the others aren't (that's also most of why they're more expensive). They all have very high quality construction, which some of the others don't. They all make somewhat more power than the others on the market, on average, or at least that's what the various dyno results graphs posted on the Intarwebs seem to show. Certainly if you go talk to folks who are serious hotrodders and weekend racers, and who are not budget constrained, they overwhelmingly choose one of those three. Check out Corvette Forum C5 and C6 Forced Induction forums, or LS1Tech Corvette forum and see.
Of the three, the LGs make a bit more midrange torque, but use slipjoints. The AR and Kooks are a very similar design and are a little better at top-end power. The Kooks are better-made than the LGs, and the ARs are better-made than the Kooks, in my humble and non-expert opinion. I'd also say that the LGs are going to have the deepest, most "traditional" sound, the Kooks something in-between, and the ARs a more high-pitched, exotic-car sound.
You should also consult your installer. They all look good sitting on the floor, but there can be LARGE differences in how well they fit, and hence how hard they are to install.
I will also say that the factory C6Z06 exhaust syste is probably the best ever put on an American car. If you are going to leave the engine otherwise mostly stock, expect little gain other than the sound (which can be sufficient reason). Headers on a car like this are not a very cost-effective mod.
For myself, I have ARs on my C5 and I'm well-pleased with them. If I buy a C6Z06, which I'm seriously contemplating right now, and if it gets headers, they will likely be LG Pros. I want that mid-range bump.
Good luck with whatever you choose.
