Sniper has 211m matches recorded, and that is not a surprise!
I'm certain that Sniper has been the first hero for most of Dota 2 players! This is especially likely, since you are taught how to play this simple hero in the tutorial. Sadly this hero is mostly popular only between new players. The sniper is what people call a "Glass Cannon": Hits like a tank, breaks like a porcelain tea cup! And because good players will most likely figure out a way to approach the Sniper at close range (SB charge, invisibility, sneaking from the back), Sniper is not a popular choice in high rank games.