Though I think this thread is a little bit "who's your favourite Spithe Girl??!" I'm surprised no one's mentioned Anders or Mr DeFarfalla yet.
Anders wasn't the most "impressive" drummer in the world, but there was so much charm to his modest approach. There was something really warm about his style - particular things he chucked into the mix still have me grinning today. For example, at 6 mins or so into Forest of October before that insane chord progression (which, btw, almost reappears in Black Rose Immortal) he'd pull out this "ta-ta tatatabombomta, bodombodombodom..tisssss" - so ridiculously simple and bland, yet so rich with character!
As for Johan, I don't think Morningrise would have been as magical without him. Just think of the acousitc passage near the start of Advent (about 3:30) or the "invisible eyes - red reflection" one in Nectar. His contributions breathed this energy into Morningrise which, in my opinion, it couldn't have done without.
That said, I'm glad he wasn't there for MAYH because he probably would have taken too much focus away from the rest of the music, and MAYH was perfect.
Anyway sorry about the excessive amount of text - I don't post here often enough and today felt the urge to get some of the excessive amount of Opethness out of my system.
Oh, and I vote Fredrik cos he's the new kid and I know what that feels like.