I'd put the service and terminals just about equally bad for both right now, so it really depends on destination. For example, if you're going to SFO, UA is going to have a better schedule than AA (and VX is going to have much better service). But AA is the only one of the two with flights to SJC, and it has much better MIA service than UA.

Both airlines have a lot of very bitter employees and both seem to be in the commodity business rather than a service business. I wouldn't let a bad or good experience on either airline influence the decision unless that decision is to stay away from both and go with an airline that is committed to better service.

Lounges, UA has more at ORD, but AA's is large and has both a quiet room and a kids' room. The kids' room benefits everyone in the lounge, not just parents. And the AA lounge attendants offer much better service than their UA counterparts, who can be downright surly.

I find UA miles to be a lot easier to use for intentional award travel than AA miles, which is a reversal of the situation about a decade ago. UA also has much larger economy plus sections than AA (I've been in regular economy seats for my last three flights on AA).

What are your regular destinations?