Not that I have much experience with these things, afterall this is my first ever online league, but I give top marks to the LBA (
http://www.laseron.org/ ). The other GMs have been great to me, fun to talk to and very helpful as I tried to learn my responsibilities and such. The commish though puts in so much time I have been blown away. Just as an example, he goes to the trouble of hand-editing every player!
Anyway I know others have pointed the league out but I just wanted to confirm what some of the others said here. So far I am having a blast and this is coming from a guy who swore he would NEVER play in an online league. It has been the perfect blend of fun and seriousness. However unless you enjoy fictional baseball this may not be the league for you (I prefer it myself).
Oh and thanks for all your hard work Lloyd. I hope this is as much fun for you as we are having.