I listen to Return to Northmoor. I enjoy it quite a bit. I also like the rather narrowed focus that it has. I will be cheering them on for this.
I've listened to Order 66 off and on and there are some things about it I enjoy, but the hosts just absolutely rub me the wrong way, so I can't stand listening to it that often. It's ridiculously popular among almost everybody I know who plays Star Wars RPGs though, even some of my local SW group listens (and they don't do much online RPG stuff at all, so that's saying something).
The other 3 I haven't even heard of.