I've decided to go with DL. In the past (post-CP expiry), I've moved about 300K to DL and have been relatively satisfied with their front cabin service. I've used the points primarily for leisure travel, LAS, SFO, MCO out of YYZ. So before Dec. 16 I'm going to move the majority of my MR points (about 250K) to DL and cross my fingers that it's the right choice.