Most people want to keep their shield size down to a minimum so that they're harder to hit, but not you. You're a titan. You're a beast. You're a hero.
The Heavy Shield's capacity of 562 and regen of 30.35 p/s are well balanced. The Flex Shield offers high regen but low capacity, the Shell Shield has high capacity but low regen, and the Turtle Shield has slightly lower stats for fewer slots but a mobility penalty.