I don't PK, but I read forums.
They say Barb survives the best, but BM kills very good,
and has more stuns than his/her oponents would like.
And with Axes has good AoE's.
They also say that R8 on BM is less dependent on
recast stats (not completely independent), and R8
in any case gives +25 Atk/Def levels.
But it's also easy to use LA helm and wrists
without restat, together with Pan Gu and Lunar
Cape have 3.33 base aps on Claws.
Maybe in that case R8 is not needed?
My good friend was BM and I was Sin, we were
on Nightscream Island, out of 8 fights he killed
me 7 times and I killed him 1 time with lucky crit.
Have no experience with Archer or Barb, nor with mass PK.
Those were just my 2 cents.
Someone with more PK experience might help you better.