Ranked by the people who log back in tomorrow
SMP is survival multiplayer: the vanilla game kept vanilla, on a map other people already live on. Every server on this board is ranked by the players who log back into the same world tomorrow, which is the only review of an SMP that means anything.
The world
Before you build anything
Everyone writes semi vanilla. For some that means untouched recipes and a claim plugin, for others it means custom enchants, mob stacking, keep inventory and a shop that sells diamonds. Neither is wrong, but read the spawn signs before you commit a week to it, because plugin soup plays nothing like the game you came back for.
A claim system decides whether you build where you like or where you can afford. Ask how you claim, how many blocks you start with, whether more comes from playtime or from a store, and what happens to your base if you stop logging in for a month. Servers with no claims can still be excellent, they just ask a lot more trust.
A three year old map has roads, a spawn town, shops with stock and someone who will show you around. A two week old one has none of that and every biome still unlooted. Ask when the world was created, when it last reset, and whether the players get a vote on the next one, because that single answer decides how much of what you build survives.
Game mode
SMP is short for survival multiplayer, and it is the plainest thing on this whole list: ordinary Minecraft survival, on a map other people are already living on. You punch a tree, you sleep through the first night, and by the second week you have a house, a farm, a neighbour two hundred blocks away and a reason to walk to spawn. Nothing is handed to you and nothing wipes on Sunday.
What differs between servers is everything built around that. Most run a claim plugin so nobody can break your walls, a shop system so the diamonds you cannot use turn into the iron you need, and a spawn town where players sell from their own stalls. Older worlds grow nether highways, public farms, community builds and a road network nobody planned that ends up being the best thing on the server. Some run a whitelist or a short application, which sounds like a barrier and is usually the reason those worlds are still standing three years later.
A good SMP server is the one still there when you come back. That means moderation that answers, rollbacks when somebody does get through your door, uptime that survives a Saturday evening, and honesty about the map: how old it is, whether it resets, and who decides. The servers at the top of this board are there because the people living on them keep voting to keep them there.
Common features across the board