As a former open composter-it's still my favorite way to compost;however, where I live now I don't have the space in my backyard to compost like that anymore. So, since bins are the only way I can make compost, I can honestly recommend two large bins for a small to midsize garden to make your compost in.
P.S. Don't forget to put holes in your bins for drainage. Sometimes a rain shower might sneak up on you and you might have to tilt the bins to get the water out. If you don't mind tilting the bins then don't worry about adding the holes.