I didn't like GR too much until recently...I started to listen it alot and now its in one of my top 5 Opeth albums.
Voted for GR, but could have voted for BW. I sadly think that WS is their weakest album overall, after many, many, many spins.
2 of my 3 favorite Opeth songs are from Blackwater Park (Blackwater Park and The Drapery Falls), but I think Still Life is still the strongest album.
Ghost Reveries, then Damnation, then Still Life, then Blackwater Park. Although I must say that Opeth turned the corner at Still Life.
It's always changing for me, which I guess is why I'm such a huge fan... These days, it's Orchid, MAYH, BP, Deliverance, Ghost Reveries, Watershed
I must say I'm surprised Still Life is winning ahead of Blackwater Park, but I can't argue with it. It is simply their best album, and has been my favourite for years.
Still Life is shoulder to shoulder with Blackwater Park for me, but mostly I love BWP and that one is very special for me in any way.