What you experienced is a typical UA nonevent. In other words, that's normal for UA service nowadays. Overall, I don't see drastic differences among AA, DL, and UA, but in specific service areas, each airline has its quirks, strengths, and weaknesses. If lounge and F menu (also the ability to preorder) are important to you, stick with AA. I have been content with AA myself, but when I first switched most of my flying from UA, I had to get used to AA's inferior mobile app, more rigid SDC (instead of UA's 24H change), and lesser award redemption. UA is better in those regards, so YMMV.