The highest level shields are generally the best. Block strength determines how much stamina a block eats, and also determines how much stagger damage you take. The bronze buckler will no longer take you to end game.

Parry is much worse off than the early days. It consumes an extra 20 stamina, which will burn your bar out very quickly in battle. Standard blocking is convenient all around and works well for single player. Tower shields have a bit of extra block power, but the speed bonus hurts it badly. Try them in multiplayer with friends.