Well, you're pretty much limited to one of 4 options with the header. Calmini, Hawk, Thorley, or build your own.
By the look of it though the Hawk one looks like it might be a slightly better design with the longer primaries (better low end torque although tri-Y headers are somewhat odd compared to say a 4-1 header in that respect).
I have the Calmini one though and can't say anything bad about it so far. I would probably avoid the Thorley unless you're in California since it's CARB certified and the other ones aren't. The reason that I didn't get the Thorley is that the location of the O2 sensor on the Thorley one only feeds off two cylinders instead of all four so your 02 readings are going to possibly be a little bit off vs. the Calmini style where the 02 is reading off all four cylinders.
Might not be a big difference really but it just makes more sense to me to put it where it is on the Calmini headers. I belive the older Calmini headers which are pretty much a copy of the Thorley otherwise also had the O2 sensor upstream of where all four pipes have converged into the collector.
