Here's UA at Stapleton - lots of Saul Bass branding and that red carpet that used to be at a lot of the UA hub gates. I miss that from meeting relatives at the airport back in the 80s.
As an avgeek UA was my favorite - a flying museum of old liveries, way overindexing on fun widebodies, airports with lots of traces of old branding, and still flying some of those great orange sunset 80s interiors right up into the merger.
For joe public that doesn't care about that stuff or even your time pressed domestic road warrior the 70s/80s strikes, 2000 SFH, gutting of the domestic network post 9/11 just added up to a bad / left behind reputation. UA valiantly found a niche post 9/11 primarily super serving heavy intl biz fliers to Asia to compensate for a much smaller domestic network than AA - which also dovetailed well with value seeking fliers who love upgrades to the big intl seat.
Crandall's AA avoided most of the really ugly stuff UA saw in the 80s/90s/early 2000s - the lesser bad of the two generically large airlines reputation wise.
DL had the best cust service reputation 70s/80s/90s - took a break early/mid 2000s and got it back post merger with AA's domestic scale to boot. CO had a great service run and reputation for its size the Bethune years.