I'd go with some ironsworn. Groups of 10, a bunch of them. If your opponent is running blocks of things like witch aelves, bloodreavers, blightkings, plague monks etc, any unit with a high volume of hits, the mortal wound on a 6 natty save is going to take chunks out of them, even if you lose a unit. They can also do that beautifully when chaffing up long range artillery, maybe some fireglaives behind them so you can nuke things as they get close. That way you can leave the bulls to go out and be play mock gore grunta while the big guns clean up and keep them safe