Best is obviously an OEM one..... end off
but if they are thin on the ground then any copy may be ok, any of them may be fine and any of those might need a small amount of fettling to fit.
Be careful/wary of the size of the aperture on the non gen' ones if your fitting an a large tipped aftermarket exhaust as some of those Zorsts are pretty big i.e. mine is. Not a problem for me as I have a OEM .:R32 rear fitted to my Eddy and the 100mm BCS .:R32 style exhaust tips fit it a treat.
As for which zorst.... BCS. Nuff said. All links and pics in my build thread.