Yet another personal opinion thread that can have little factual resolve to it, being a question of which drummer is preferred. Posting it on Opeth's forum raises Martin Lopez' bias, just as posting this same question on a Dream Theater forum would raise Mr. Portnoy's. With the various equipment differences and song styles, it's very difficult to objectively differentiate a drummers ability and style from the aforementioned elements.
With that out of the way, the superior songwriting and musical ability of Mikael Åkerfeldt and Peter Lindgren would make less-than-stellar drumming a non-issue. However, Mr. Lopez carries his hefty responsibilties out exceptionally well. In my estimation, he adds to the band, rather than playing along with the intimidating figures of Peter and Mikael, as I feel many drummers would.
Mike Portnoy is the intimidating figure of Dream Theater, and with conviction. When compared with Opeth, Portnoy's band cannot compete, though. Would Portnoy thrive in Opeth? Would he out-do Lopez? Would Lopez create the same aura that Portnoy has in Dream Theater? Speculation can lead anywhere. With the discrepancies between the bands, Lopez is given the nod.
r is right, l is left and a * I was using as a cymbal hit. What you've written there looks like some kind of disabled, monstrous ratamacue 
