Um, back to the size and temperament thing.
Brown Swiss are one of the hugest but also one of the mellowest cows around. I can't imagine mine hurting me. All they want is food.
It seems to me the smaller things are the more frightening they can be, for example, chihuahuas, Napoleon, ponies (what terrible temperament they have!), bantam chickens, and... miniature Herefords? I don't know about that last one because I haven't had them.
There's probably not a real relationship between size and insanity, but that's just my prejudicial rule of thumb. And yes, I'd rather plow with oxen than horses for the same reason.
For me, in choosing cattle, the most important thing was temperament. They are huge and I don't want them dominating me. Since it's only a prejudice, I decided to do some research on breed versus temperament, since it would be more accurate. I started at
http://www.ruralheritage.com which led me to the OSU web site on breeds,
http://www.ansi.okstate.edu/breeds/cattle/ .
Food and milk were secondary issues for me, my primary concern was getting oxen to plow fields. I'm still a few years off from that, though...