Personally, I'm just not a fan of AR headers. I don't like the fact that they're not equal. The drivers side makes a turn with the tubes, then there the collector. The passenger side goes straight back like the Kooks and SW's do. They do that so they can put the crossover pipe infront of the trans pan. I don't think it makes that much of a difference IMO where the crossover pipe goes. The Kooks crossover in the middle of the pan and the SW's crossover at the rear of the pan.
It's true we can't use the AR's with our turbo kits.
I have been running the SW's for 3 years now. Love them. I will say this, watch out for cracks. Granted I had an old set, I don't know if anything has changed in their manu. process. I was getting some ticking sounds and we replaced my gasket only to still have it. When we did the turbo kit, that's when we found the cracks in the welds. A simple weld around the outside and all has been good. They do offer a LifeTime warranty but we managed to fix them in about 30 mins.
I would say with the Kooks, you get what you pay for. BlownWK's were fantastic looking still when we removed them for his turbo install. Any set you buy are going to all make about the same power. I don't really see one set making anymore power than the others. I would love to see one of them prove me wrong.
Would I buy the SW's again..... yes I would. Like I said, I've had them for 3 years and they still look great. Other than a few cracked welds, they're still rockin'.