Are we voting for what we perceive as the best benefit of Mileage Plan relative to other frequent flyer programs, or just in regards to Mileage Plan?
Perhaps no definitive answer?
For example, I feel that the best benefit relative to other programs is the change fee waiver, this benefit is what sets Mileage Plan above all else. But as far as best benefit not considering other programs, it has unlimited complimentary upgrades.