Like oil... which exhaust is best, is subjective. There is no conclusive facts of a dyno header shoot out, side to side.
Different day, different dyno and different ambient conditions all will give skewed results.
What Brock shows for gains with a pipe and dyno time is almost not believable. Gains like that are so very rare. Bu if you buy in to that, maybe Brock is the best. Although it may not be a torque pipe.
Different brands, bends, sizes & restrictions net different results.
I think Akrapovic is the best made and best results pipe. But it looks too stock for me.
Zard is an interesting looking pipe and they usually work well.
I went a roadrace pipe for looks, and tight fit. It will never drag. It has period correct looks. As it is not a mainstream exhaust, who knows on what kind of power it makes.
Its mapped and hauls ass through the gears to 130 mph.
Good luck in your decision!