ADToE, by far.
As someone else mentioned, DT12 has not aged particularly well to me.
My theory is that, because they opted for shorter, more concise songs on DT12, it is far more likely for them to lack as much replay value as their longer, more intricate songs.
This isn't a knock against the shorter songs, as I do really enjoy them for what they are. BTV and STR are still amazing songs that I continue to listen to.
ADToE is an album which I can listen to from start to finish, and enjoy almost every moment of.
I cannot say the same for DT12. I very rarely listen to FAS, EM, or TLG. These songs are just underwhelming to me, especially for DT.
Rather than knock DT12 though, I will just say that ADToE is one of my personal favorite albums of all time, by any band, so DT12 has huge shoes to fill for this poll.
The great thing about ADToE is that I honestly did NOT expect it to be very good. The band was in a weird place after losing Portnoy, with Petrucci programming the original drums synthetically and such. I did not have much hope for the album at all. But it blew me away.
BAL, BITS and LNF are perfect examples of why I love DT. Amazing metal riffs, epic moments, beautiful keys/synth layers, incredible vocal melodies, and lots of different parts which give the songs a ton of replay value.
DT12 has some amazing moments as well, but one big disappointment for me has been Illumination Theory. I can say, since it's been a year now, that IT has sadly become my least favorite DT epic. Still a cool song, but pales greatly to Octavarium, Six Degrees, Seasons, etc.