kassadin

LeBlanc has 2 mobility spells. If she uses them for mobility, she loses out on most of her damage until they are off cooldown. At 18, they have a cooldown of 10 seconds and 24 seconds respectively, and her entire combo relies on both being up.

Kassadin has 1 mobility spell. At max rank it has a 2 second cooldown, and can consistently be used 3+ times before you would ever worry about mana. If it is on cooldown who cares, as it will be off cooldown VERY shortly.