Best server environment for playing unity game?

50k players of "Chess" won't need the same performance that 50k "Shooter" players need. You won't get a valid answer this easily. Besides: 50k concurrent users usually require 100x monthly active players. You sure you get half the success that WoW has?

Anyway.. What type of servers are there available to use? I want to make use of it too. I saw somewhere a reference to the MySQL language too? So does that mean an Apache server would work?