What online multiplayer PC game you play and like

Hi!

What online multiplayer PC game you like and would be willing to take part in the tournament?
My idea is to gather info about games that you like and maybe start a tournament! But first I want to make a poll so we can decide all on what game we pick. :)

It can be also an old PC game... My list:
League of legends
Counter-Strike 1.6 / GO
Unreal tournament (gold edition) - if i remember correct. old game
Medal of Honor: allied assault
Worms: Armageddon
FIFA?
XCOM 1

Please suggest your own list... It can be online free games or paid games.. :) If you remember another game you like, please write it as a new post!