WCIII TFT is quite easily blizzard's greatest game simply because of the world editor.
I have played a bit of WoW, SCII, and Overwatch, and nothing will come close to finding a new custom game Sunday morning at 2 am and having fun with a random lobby.
The "melee" (standard mode) matches were great too.
I have played a lot of games and genres and nothing will ever top that experience for me.