In my personal experience (I've been keeping up aquariums - both salt and fresh - for a number of years), freshwater angelfish are some of the most hardy I've come across. They've outlasted any other fish I've put into a tank and they're some of the prettiest out there for fresh water (when you're looking at affordably priced fish, anyway). I've had angels live for years. My last pair lived for a couple of years and laid eggs frequently. They might still be living for all I know, we had to give them away when we moved recently.
Mollies are apparently really hardy too, but they're really prone to developing ich and so I just avoid them. Betas can be pretty hardy too, but they don't always play well with others (especially other betas). While freshwater angels can be aggressive, they've lived relatively peacefully with every other fish I've ever paired them with - just make sure you add fish that are considered "community fish", otherwise, they might be too aggressive and nip at fins too much.