I have all the hats for all boss hunts but I still love to play boss hunt, it is still fun.
For collecting rainbow stars, I simply play a normal level with random, as more and more players know about it. If they don't, I will do my best to communicate the strategy as we go along. If the team works well and nail it, I will play a hard level with them.
For crazy level, if the random team is really good, why not try with them. Otherwise, I will invite friends to do it.
Note: I have a group of friends that love crazy level boss hunt as well, so I will just wait for their invitation.