Sadly I only got to "Opt in" to the server when I got to level 28 :/

Vanilla?
No:
1) You can a certain amount of land that only you and people you trust can access
2) Mobs spawn in with random armor (can be dyed, enchanted) and weapons (eg: skeleton with a chain helmet and diamond sword)
3) You can set home
4) Mob griefing is disabled
5) Ores have a chance of regenerating (I mined the same piece of diamond more than 3 times once :D

Pros:
1) Great community
2) Friendly / Welcoming people
3) No griefing at all as far as I know
4) Players help you
5) Great builds
6) Nether reset monthly so you get tons of glowstone/quartz

Cons:
1) You need to get to level 10 in Planet Minecraft. If you want help, I have some here:
http://www.planetminecraft.com/blog/how-to-get-lots-of-xp-in-planet-minecraft/

Diamonds make me happy :)