While the top-tier phone service (and Admirals Club agents) are great for AA, I don't think there's a huge difference for 1k's.

THE big advantage (IMO, again) to being EXP on AA over UA's 1k is the 8 systemwides which are valid on ANY fare bucket (and good for up to 3 segments). I've only once had one not clear. Additionally, it's my experience that AA does a better job of availability of cheap award seats for its EXP members than UA.

Domestic upgrades AA vs UA seem about the same, some minor quibbles over the fleet (E+, IFE, food, routes, etc) which makes being low- or mid-tier a more even proposition to me. I would (and will) go out of my way with my $'s and personal time to make sure I'm AA EXP. If I absolutely couldn't make EXP, I would have a very hard time deciding which program to devote myself to.