Shields are a noob trap. Better to get dual-wielder feat on casters to dual wield 2 staves (Hag Staff, Sparkler, Rainmaker and other good staffs are available easily in Act 1 and only get better). You end up with much better net stats and similar AC, as well as more unique magic item slots. Melee should be using 2-hand weapons.

Only person that should use a shield is a ranged striker, which will always have a level in either fighter or ranger so will already have shield proficiency.