I have both (lucky me?).
I find that the compulator works great for strong, over the top effects like the EHX BMS or the Fulltone Choralflange. These are the effects that sound like they are going to distroy my speakers. The flanger gets going and it's almost like a carnival ride.
But for general compression duties I find that I like the multicomp. It really seems to add some flavor to my tone but I can't explain what.
I guess if I could only have one it would be the Demeter for the protection value it offers.