I fly 30-50 times a year, sometimes more. ALL work related. While I fly mainly on three airlines, I hit all of them eventually. And it is all just a numbers game. About once every 20 flights or so, something gets screwed up with my baggage. Airline makes no difference. Crappy service afterwards? All of them.
I have become a master a compaction and try to use carry-on baggage whenever possible. You have less legroom, but less chance of loss with one of the smaller jets that you check your bag at the end of the ramp. Even if I am checking baggage, I also have a carry-on that has everything valuable in it as well as enough emergency supplies to get me through a day or two.
I flew American Airlines last winter and Jet Blue last spring and United in the summer... AA and Jetblue were phenomenal. Unless I have not choice, United has lost my business, as little as it may be, and I will share when possible how awful they are.