Across 573 ranked games on patch 16.21 in Master and above, Varus mains win 52.0% of their games in the bot lane.
Their most common build appears in 33.7% of those games and wins 49.7% of its 193 games.
It starts 
two Health Potions and 
Doran's Bow, completes 
Statikk Shiv, 
Guinsoo's Rageblade, 
Terminus and 
Jak'Sho, The Protean in that order, and takes 
Gluttonous Greaves.
Three other builds are played often enough in the bot lane to be measured on their own.
In the bot lane, Varus mains fare best against 
Zeri (won 68.8% of 16 games), 
Ezreal (won 65.0% of 20 games) and 
Jhin (won 54.8% of 31 games).
Their hardest matchups, the champions that counter Varus, are 
Jinx (won 37.5% of 16 games) and 
Draven (won 45.5% of 11 games).