Across 1,528 ranked games on patch 16.21 in Master and above, Rengar mains win 53.3% of their games in the jungle.
Their most common build appears in 60.8% of those games and wins 52.9% of its 929 games.
It starts 
Gustwalker Hatchling, completes 
Umbral Glaive, 
Profane Hydra, 
Lord Dominik's Regards and 
Infinity Edge in that order, and takes 
Boots.
Two other builds are played often enough in the jungle to be measured on their own.
In the jungle, Rengar mains fare best against 
Cho'Gath (won 69.7% of 33 games), 
Jarvan IV (won 65.7% of 35 games) and 
Qiyana (won 63.2% of 38 games).
Their hardest matchups, the champions that counter Rengar, are 
Lee Sin (won 39.4% of 71 games), 
Kindred (won 35.0% of 20 games) and 
Shaco (won 30.8% of 13 games).