I can't say Mikael or Peter, because, as musicians, they aren't very versatile. They can't read music, which kind of subtracts from it all (for me). I mean, for the guitarists here who've heard Mike talk about the more technical aspects of what they do: "I bought the amp because it didn't have a lot of knobs on it." It seems as though he just writes and plays, and doesn't know the details, so to speak.. Though I love Opeth's music, I wasn't always as fond of Mike's songwriting style as I am now. I used to think it was kind of lame that he doesn't know where a song's is going. I used to think he made his songwriting style sound "artistic" by saying he pieces it together like a puzzle, or their songs just "turn out" as long as they do. I mean, I think songs like By The Pain I See In Others are like leftovers that Mike didn't want to throw away, but didn't really sound good anywhere. Now I have more appreciation for Mike songwriting style, because he's kind of like an author. He gets an idea, but doesn't really know where it's going to go. He just kind of pieces things together.
Peter is cool, but I don't think he's that good. His solos are pretty bland, and are more like fills. Take the first solo in Deliverance, for example. It practically ends on the same note it starts on. It's a slightly impressive display of technical ability, but it doesn't really take the song anywhere. The last solo in the song, which I believe Mike wrote, is very transitional, and actually takes the song somewhere. I definitely appreciate that more.
Mendez is definitely a steady bass player, but I don't think what he does shines as much as what Johan did. Take, for example, 10:20 - 11:09 on Forest Of October, and 2:16 - 3:10 on Black Rose Immortal. Mendez never sounds like that. I don't think that's his fault, though. I think part of the reason Johan and Anders are no longer in the band is that Mikael slowly realized what he wanted to do as a songwriter and musician, and he needed musicians that were more skilled, and who let him have almost total artistic control. I think in the days of Orchid and Morningrise, there was way more input from the other band members.
That's why I'm going to have to say that Lopez is my favorite musician who's ever been Opeth. Though he isn't always as tight live as he is on the album 'cause he's wasted sometimes (who can blame him?), I think that he contributes a lot of subtle and interesting musical ideas that help keep everything interesting. Anders is hardly competition. I mean, I forgot where I read this, but apparently after leaving (getting kicked out of?) Opeth, Anders quit playing drums. You know the guy wasn't that convicted, musically. Lopez rules!