To be totally candid, I am not a drumming person at all. I mean, I don't know much (anything) about music theory as is, and drums are the instrument I pay least attention to. I haven't really thought about what drum compositions I would qualitatively rank as the best. I said that for two reasons: 1) I know erwinrafael is very passionate about the drumming on IT and wanted to poke a little fun and 2) In all honesty, Metropolis is the Dream Theater song on which I notice the drumming most and think "wow, this is really impressive."
Erwinrafael, while I have no doubt that Mangini does a lot of interesting and subtle stuff in his drumming, I must say honestly that I don't have that feeling towards any of his songs. All the DT songs where the drumming sticks out to me are MP. Which should not be taken that seriously or harshly by Mangini and his fans, because it's rare that I pay attention to the drumming, and there are plenty of drummers who I know are great but also I never notice. Portnoy is more of an exception than a rule.