I think 1 horse sized duck would be easier than 100 duck sized horses.
With a 1 horse sized duck you can focus your full attention and stamina on that one creature. Yes it would be powerful but you could take it down if you fought smart.
With 100 duck sized horses you would get overwhelmed. At best with 1 good kick you could if your lucky get 3 in one shot, but you would have a lot of trouble maintaining the kicking force required to kill/incapacitate them with one kick. Then there would be the issue of them biting your legs, with time and enough bites they could easily reduce your ability to support yourself on your leg and then if they bring you to your knees, it's game over as they would simply swarm you.