Game Servers | What's Profitable?

Hey guys, now, I know games are meant for fun to most players, however to the owners of game servers, they're simply money making machines..

I was wondering what game(s) you thought were the best for income, example;

Garry's Mod
You can use ad services and get paid

Minecraft:
You can get players to purchase addons

Also, what's the pros and cons?

Garry's Mod:
LUA is annoying, buy putting ads is easy

Minecraft: Plugin Development is easy but getting players is hard