I used to play on Mocomochi, but since that's dead, I moved over to Clockworks on EU FlyFF.
Highest level on Moco was 145H, Highest level on Clockworks is 70.
It doesn't seem like there's very many active players from the jsp community. However if you were wondering what the most active server is in general, I would say it'd have to be Clockworks, since it's a little over a year old at this point.