ACOS, and it's not even remotely close. It's my third favorite DT song. I have NO clue why people love Octavarium so much. It just doesn't work for me.
Go and listen to Razor's Edge and then tell me you can't figure it out. That to me far exceeds any part of ACOS.
I find that ACOS has much better lyrical continuity and flow, especially as Octavarium doesn't intend any as far as I can tell. It's a couple of unrelated stories, then some random juxtaposition of name dropping, then a summary of the album. So obviously ACOS is going to connect a lot more emotionally for a lot of people, having a very personal story behind it.
But I find Octavarium has much better musical flow. I know what you're thinking - "BlobVanDam, you crazy". But just hang on for a sec. Octavarium is sort of like 5 or so big musical sections that aren't related, kind of stuck together. But musically, these sections flow into each other pretty well for me. And for a 24 minute song, these few transitions are pretty well spaced apart, and done well.
ACOS on the other hand, feels like dozens of little musical sections stuck together, and while they mostly flow pretty well, I find it a lot more jarring for the emotion of the music, because it doesn't build as long on each section.
Obviously both approaches can work equally well or badly, as it comes down to the specific song. But for these two songs specifically, Octavarium does it better than ACOS imo.
Of course, I'm talking musically here, as I value that much more than lyrics. Lyrically, I won't at all argue that ACOS trumps Octavarium. Different strokes.