Draft Kings is great fun because you pay a small entry fee for a week and “draft” a team under a certain salary cap. If you’ve got a bit of knowledge it’s not too difficult to get in the paying bracket!
I also use fleaflicker.com for dynasty leagues, really good because it’s so customisable!
Fleaflicker is underrated and really simple to use. It’s great. They allow you to do things that some of the mainstream sites don’t, for example pre-draft pick trading is permitted and easily enforced, etc.