I'm registered over at Blue Moon, but I've never really been active there. I went because a friend asked me to join a game he runs there, but then he dropped out of circulation, so I never bothered to go any further.
I prefer E for a whole load of reasons, most of which have already been mentioned. But a big one is aesthetics. E has clean lines and is organised. Blue Moon...well, there are no limits on the size of avatars and the like, so it always looks jumbled and messy to me. It used to give me a headache just browsing a thread!