I too think the DL upgrade system is superior to its competitors. As a twenty year in a row UA Elite (either the equal of Gold or Plat.), it's just plain easier and less stressful to get upgrades on Delta. My upgrade percentage on DL this year is 66%, but only about 50% on UA. Rarely do UA upgrades clear outside of thirty minutes before push-back, and I much prefer the DL "gate lottery" system of determining your chances.

One thing I've noticed that is similar about the two programs is difficulty achieving upgrades at certain fortress hubs. Upgrading while originating in ATL on DL, IAD or SFO on UA, is always a challenge for this mid-tier elite.