I want to 2nd the following
CO: Three things stand out for me with One Pass: 1) Best Unlimited Upgrades for domestic service 2) 75K threshold for the top tier,and 3) the numerous OP mile bonus' that they consistantly offer
CO: Worst: HoKeY fares for upgrade lottery. Its the lottery part that I find are the worst, not so much the higher fares to u/g
DL: Best: Two things Plats getting Free CRC and ease which I've been able to redeem Free travel awards
DL Worst: far and away not being able to up grade on L/U fares (this was one of the main factors for me switching to CO)