Big fan of cows, would like to have on eventually. What do I need to know?

Any cow I got would be a pet, not just a pasture ornament. So what breeds are the hardiest? Friendliest? Health care? General care" I'm not planning on getting one until I know everything available so don't answer saying "you're not fit to own a cow, you'll never get it right". Any information is welcome! Thanks :)