There's alot of things that AA could do better, but overall they fit me well. Every airline has their mess ups, although DL is probably the best operationally from what I have read here.
For me personally:
WN - doesn't work for me as I go international about 50% of my trips
DL - not usually competitive out of OKC (I assume because hubs are farther away). Some of my travel is corporate so I have to pick the lower cost fare. And, Skypesos. (not that AA is that much better these days)
UA - Probably my only reasonable alternate - and I almost moved to them when it was CO and AA was on my last nerve. IAH would replace DFW for the majority of my connections. I can get some extra benefits on United due to my employer, but I'd have to learn the ins and outs and tricks for everything there that I know on AA.
Based on all this, it's really a UA vs. AA decision for me. I don't think AA is any better or worse than UA, and most of the time I'm as happy with AA as you can be with an airline. At the end of the day, you aren't picking the best, you are picking the least of the evils.