I have been with RN Network for 5 years and think it is the greatest. Re their insurance, have had no problems here with that. My husband had quite a bit of dental work, and several office visits with just our copay and quick payments.
All companies get the same amount of money from the hospitals, and the agency decides what your salary will be. You may get a bit more money with someone else but they may scrimp somewhere else, like housing, benefits, etc.
My recruiter is always available, and takes care of me very well. They are also JCAHO accredited. Your recruiter is they key to success with traveling. I have heard real horror stories about nurses being told one thing just to get them to an assignment then changing stories mid stream. You have to be able to trust your company and recruiter.