The most infamous sever out there is apparently 2builders2tools, which is a complete free-for-all, ganking and griefing paradise. I'm not quite ready for that, mostly because you always spawn at near the 0,0 coordinates. If it would randomize your respawn to a much larger radius it would be more interseting.
So I'm looking into poking around Civcraft's 2.0 server instead. The server is semi-vanilla, but has some different rules like "Prison Pearls", randomized spawning anywhere within the 15,000 block radius, and the ability to reinforce placed blocks using iron or diamonds. Last night there were 30-40 people online, but in my two hours of wandering, I never saw a soul.
For those looking for human contact, I have the following notes (hopefully current as of Oct 2015). But I make no guarantee of their veracity or whether the situation has changed.
- Go in expecting to get ganked, pearled, and griefed.
- Thule is an underwater city around -8000,+4000
- Mount Augusta is the current "big" city, which draws both good and bad, down around +2600,+2100
- NOX and Carson (-4400,+1500) seem to be in conflict
- Icenia is up near -6500,-6500
- The supposed map of claimed areas (moderately out of date).
- Libra, Arran, Athens, Yoahtl, Kaiserinreich, SPQR are possibly places to visit
- Avoid Mises and probably Carson and the area Northeast of Kappi (so avoid +1800,-1100)