Vi and Shen...

pretty much have the same passive...

Blast Shield STATIC COOLDOWN: 18 - 8 (BASED ON LEVEL) When Vi damages an enemy with an ability, she shields herself for 10% of her maximum health for up to 3 seconds.

Ki Barrier STATIC COOLDOWN: 10 After using an ability, Shen shields himself from 52 - 120 (based on level) (+ 14% bonus health) damage for 2.5 seconds. Abilities that successfully affect champions reduce Ki Barrier's cooldown by 4 - 7.5 (based on level) seconds. Shen's power manifests as a Spirit Blade that he can control with abilities.

Functionally, they are pretty much identical... I mean yeah, Vi's is a bit better if both were to forego building health but overall Shen's is preferable because of the health scaling and shorter cooldown.