I can highly recommend this league.
I joined at the start of the KBL's third season and I have loved every minute of it (even despite the fact that my Timbuktu Colobus did just get run out of the first round of the playoffs).
Kieran is an incredibly dedicated commissioner and he really puts a lot of time, thought and effort into making the league a fun, competitive and fair experience for all owners. Jeff does a great job as vice-commissioner and all the owners in the league are very friendly, knowledgeable and mature. The forums are active and several owners even post entertaining updates of their teams on a regular basis.
This league has an interesting lore and history. The fictional teams and players all have a well-established sense of identity and it really adds to the overall enjoyment of the league.
If you're looking for a good, solid league to call your OOTP home for many years to come, you couldn't do better than the KBL.