I was only really concerned with how they did at United/Madrid and Internationally;
In his career at United, Hernandez has scored in all competitions 50 goals in 117 games. A goal every 2.34 games.
Higuain at Real has scored 122 in 266 games, a goal every 2.18 games. (and 46 assists)
Internationally Higuain has 20 goals in 32 (and 9 assists), meaning a goal every 1.6 games.
Hernandez has 35 in 53 meaning a goal every 1.51 games.
Higuain's club form is superior and over a great period of games which makes it more impressive, he also gets more assists which ties in with him being the more rounded, technically superior player, based on current achievement.