What is the best game to play online

There's absolutely no way anyone can possibly answer your question due to the ridiculously vague nature of it. What console(s) do you have? What genre of game are you looking for? What's your age range? Do you want co-op or competitive? If you don't own the game, how much are you willing to spend on it? Even if we knew all of these things, the "best" game is still completely a matter of opinion.