I love Chesscube particularly because of the Warzone events in the morning and evening. Unfortunately it means I'm burning the candle at both ends if I try for both!. The Tournaments make chesscube very special and the integrated social chat rooms - are much more lively than more established servers. The social element is strong.
The cubits and crowns system is interesting and adds a bit more spice for the virtual tournament prizes.
Of course, the Kingscrusher cafe is great personally for me, and generally the encouragement of other v-bloggers or bloggers like Chessnetwork too.