It probably depends on what you're looking for.

Even with some of the things that have gone wrong, or downward, since 3/3, I still don't think UA is the worst by far. I still get treated well on UA, and more than that, when things do get wrong, they are generally very willing to help make things right.

I've never flown Spirit, but from everything I've heard, yes, they're worse.

In terms of the ones I have flown, I'd say Delta is by far worse than UA. I live in CVG, so occasionally have to pick up a RT on them a couple of times every year or two. And everytime, they give me yet another reason why I purposely don't choose them unless I have to.

But as always with this kind of thing....YMMV, I guess.