If sustainability is your goal, skip beef and plant a decent garden where you were going to run the cattle. ;-) You can grow a lot more food by planting seed than you ever will by converting grass into beef on ground that could be farmed.
Pigs do okay if you have enough scrap for them but once you have to open a feed sack you're better off buying pork at the store. Egg laying chickens that will forage are cheap protein as long as you can keep them close enough to home to find the eggs and they're turned out to pasture so You don't pay to feed them. The commercial type meat chickens won't forage so you'll wind up feeding them out of a sack and spending more to make a meal that's the same as you'd buy over the counter.
Turkey's are fantastic as you can turn them loose and they stay close by, don't make a mess, don't eat up your garden as bad as other birds, and they're fairly easy to catch. Plus you get a lot more bang for the buck cleaning a turkey for dinner than you ever will on a chicken.
If you decide to milk something, go with a goat... much more efficient for a small family. We get about a gallon a day.
That all being said, we eat two steers a year without much corn influence and have plenty of ground beef for the rescue mission. I wouldn't do them if my goal was to feed the family in the most efficient way but we have the ability to put grass in front of them year round above and beyond where we have our gardens and other livestock so we do it.