I have been fortunate enough to travel only in F on domestic flights over the past 6-7 years. My opinion here is based on CO, UA (both pre-merger), DL, NW, and AA. About 75% of my travel was on CO (prior to the merger), and 100% of my post-merger travel was on UA.

I find that, apart for more legroom, the level of *service* offered in F by UA and CO was the best. AA comes a close second. DL and NW are (were) far behind.

This said, the level of service in F today is no different (again, apart from legroom) from what I used to get in Y back in the 1980s.

In terms of international business class, I flew CO, AA and AF over the past six years. I would rank them as follows: CO>AF>AA.

So, when asking if there are any airlines worse that UA, one would have to specify: on what dimension? If the dimension is service in domestic F and international C, then, you sure can find a lot worse!