IMO, any MP Greatest Hits has to include at least ONE song from each of the following Non-DT acts:
Liquid Tension Experiment
OSI (first two albums)
Transatlantic
Neal Morse and/or Morse/Portnoy/George
Adrenaline Mob
Flying Colors
The Winery Dogs
The live covers band stuff isn't totally necessary, but if you wanted to do a disc of live covers and throw in some studio covers he's done with DT, TA, Neal Morse or MPG, then that would be fine. And if you pick from Cygnus & The Sea Monsters, why not got for "YYZ" with the drum solo? Perfect showcase for Mike! I mean, it's a compilation all about him, right?
Also, any DT songs should likely be songs he wrote lyrics for, or at very least, has a large part in it drumming-wise, or vocally. Probably anything between FII and 8VM would be great.
In the end, I'd say if it was a 3-disc set (because his discography is so huge), the first disc would have to cover DT/LTE/OSI/AMob, the heavier stuff that he's been known for; the second disc would cover Neal's stuff, TA, Flying Colors, TWD, the more melodic/proggier stuff; and the third disc could be a covers disc, pulling various studio and live covers that he's done, just to show that Mike is a huge fan of music, and a great way to show off his influences and inspirations. Also, you can't forget the MagnaCarta covers albums he participated in, especially
Working Man, which if I had to include ONE song from there, it would either have to be "La Villa Strangiato" or "Jacob's Ladder", easily my favorite performances of his on that album.
-Marc.