Too close!
My favourites are IAW, SDoIT, Octavarium and DT, which are... two from column B, two from column C. The runners up would probably be Systematic Chaos and A Dramatic Turn of Events, which still doesn't narrow it down at all. And SfaM and Awake complete both sets as similarly solid and good Dream Theater albums.
So, er, I don't have an answer! "Not A," I suppose? I legitimately like both albums, but BCSL and WDADU sit in 11th and 12th respectively, and while Train of Thought is quite strong, Falling into Infinity is good-not-great.