Basically, all of the above. Ling/Hydra is probably the best and do every little thing you can to delay it. Once he runs out of energy and you have comparable armies, you won. Look for pylons, as big creep spread as possible, ling runbys after he moves out, surrounding the moving out force, baiting FFs. If you can't take the fight, just counterattack (nydus also possible) and try to break the natural while building zillion spines in your natural aka the TLO strat. If you want to feel extra fancy, you can try small counter to make him look away from his army so you can surround it before the FFs get cast.