I'm gonna go for MoP mainly cus its the song I've heard most, as that album often get a few spins on repeat, opposed to AJFA, which is imo a little bit too "we can make a solo"-ish.
And yes, One is gonna get alot of votes thanks to GH3, but well, that just made me move further away from the song, I've heard that very very long melodic intro so many times just to be killed off by that darned solo (im no master at GH at all, but its fun).
Still their best songs imo is The Thing That Should Not Be, Nothing Else Matters and The Day That Never Comes (Its the modern One really, and the video is the best ever made, ever).