I've had good experiences on DL and I've had bad (even terrible) experiences on DL.
I've had good experiences on AA and I've had bad experiences on AA.
I've had good experiences on UA and I've had bad experiences on UA.
I've had good experiences on B6 and I've had bad experiences on B6.
I don't keep track, but I don't *really* feel like one is meaningfully better or worse than the other (well, B6 has the legroom...lol). There's a lot of randomness in this and few people really fly enough to smooth that out and get a real sense if one is better or worse.
ATL-FLL definitely sounds like one of those bad experiences. All you can really do is write to DL and complain (or just never fly DL again
). Not sure of the going rate of compensation, but I'd think a 10k miles or a regional upgrade certificate would be fair-ish. No idea whether they'll actually give that.