Switching from 2-hander to 1-hand/shield is a waste from my experience. Pummel (berserker stance ability) does the same thign as shield bash and doesnt require a shield equipped and since pummel and shield bash are on linked cooldown timers pummel is more efficient.

Ideal grinding material for warriors is anything with low armor, usually caster-type mobs because you can interrupt most of their spells and take little damage from their melee.