If the tracks are scaled to the same unit (presumably one where one human width equals an infinitely small number), everyone in the top track would die of exposure before the trolley even reaches its first victim due to there being infinite distance between integer milestones, whereas everyone in the bottom track would be killed instantly due to any distance traveled having an infinite number of infinitesimals*. So I choose the bottom track to be merciful.

If the tracks don't share the same scale then we don't have enough information to make a judgment.

* Even though we already established the one human width rule. Could someone check my logic here? Infinities break my brain.