Minetown is the only 'organized' server I've found. We have a wonderful community, and some of us have been here for quite a long time as regulars. Our moderators show high standards, none of them are biased in any way, they all do their job very successfully and they are one of the main reasons why I play on Minetown.
I would say the only two downsides are the odd troublemaker that occasionally comes on and spawns chaos, and the lag (however the lag is being somewhat resolved, the owner is investing a load of money for his project to upgrade the servers).