#1 Path of Exile
#2 World of Warcraft
#3 Don't know
Reasons behind my choices. I have not played/tried anything else to be more useful. Path of Exile, free, challenging, competitive, perma death game with some economy, crafting, character progression and unique build/talent/skill system.
World of Warcraft, great overall MMORPG. Allows the player to PvE, PvP or pursue titles/achivements/collectables while content is delayed. Drawback is of course the monthly fee and expansion fee that's coming soon.
Both of these games do very good job with security. There is wild bottin going on, but it doesn't severely impact players gameplay. At least there are no hacks, so that's a plus.