Tough call between the Watershed or Pale Communion line-up. I went with the former, because of how that band functioned in a live setting, but I could have gone with either.
Note that I didn't even look at album quality or favourite tracks, my three favourite Opeth records have all been written way before this line-up existed. I think that shouldn't detract from the musician's quality, since I think Opeth has had the best line-up in recent years. Obviously Åkerfeldt has always been the principal song-writer, but it's the musician he plays with that give the band their sound.
The Watershed line-up it is!
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EDIT:
I'm an idiot, I just explained why that is my favourite
and I voted for that line-up as well. Damn.
Honestly, my least favourite would be the MAYH as well, so if you could change my vote accoprdingly, that would be great