Was EXP for a little over two years on AA and found the perks like drinks and snacks in Y (when no F service offered) great. Upgrades were always nearly automatic (especially out of IAH and MIA) too... But....

No comparison to GS on UA. The constant phone/email updates on IRROPS and staff working the terminal gates are just fantastic. These folks go "above and beyond" every day.

I understand CK shares some elements of GS but don't have personal experiences to reference.