Every carrier has its top producers, long-term contractors and happy people. So too with flashes in the pan, long-term complainers that don't do well but don't leave either, and wash outs.
At least important as the question, "How contractor-friendly is the carrier?" is the question, "How carrier-friendly are you?"
Dispatch systems, office cultures, customer bases and professional standards vary from one carrier to the next. Look at carriers not with an eye toward how good they will be to you, but with an eye toward how good you can be to them.
Find the dispatch system, culture, customer base and professional standards that you can be comfortable with, if not outright delighted, and then give that carrier your very best. Learn the system, adapt yourself to it and work it for all it is worth.