I have two colleagues who are DL 360, several UA GS, several who will make UA GS this year, and a couple more whatever the level is below DL 360.
From all the bar room debates, the conclusion that I have reached, at least at the 360 / GS level is that for service, DL is actually better, particularly for things like transfers and basic upgrades.
For a FFP however, UA seems to win hands down, particularly at the GS level.
I keep pondering going to DL, but frankly I believe that the FFP is better with UA. Other service type issues to me seem like arguing between a Bentley and a Rolls. Ok, maybe not a Bentley and Rolls, maybe a Ford and Chevy.....my reasons for sticking with UA are the FFP and that Mrs Limey gets my status and that UA are typically fairly nice to her.
Oh, and the GS skip the lines at security at various airports are the best.
Good luck, please let us know where you drop, and why!
G