I have worked for a few airlines and looked a good many that are operating. The ones that have had the best conditions are the ones that have a strong union affiliation. If you join a small airline then you may as well represent yourself, but you will be at the besk and call of the company, because that is what small airlines/company's are like. If you end up at one of the major/larger airlines, at a guess one with 200 or more flight crew 20+ aircraft/ international routes then you need a union like you need oxygen. There is no point in trying to represent yourself you might as well try adn push butter up a porcupines rear end with a hot needle.
In short if the company you join has union representation, balpa, IPA, or whatever join it.