Across 2,008 ranked games on patch 16.21 in Master and above, Hecarim mains win 54.6% of their games in the jungle.
Their most common build appears in 51.4% of those games and wins 55.1% of its 1,032 games.
It starts 
Gustwalker Hatchling and 
Health Potion, completes 
Spear of Shojin, 
Death's Dance and 
Endless Hunger in that order, and takes 
Ionian Boots of Lucidity.
Two other builds are played often enough in the jungle to be measured on their own.
In the jungle, Hecarim mains fare best against 
Darius (won 76.9% of 13 games), 
Kha'Zix (won 62.5% of 56 games) and 
Qiyana (won 59.7% of 62 games).
Their hardest matchups, the champions that counter Hecarim, are 
Shyvana (won 29.4% of 17 games), 
Gragas (won 27.3% of 11 games) and 
Master Yi (won 38.5% of 26 games).