I spread some clover in areas where I wanted deer to come and take a bite, and then head out to a field. I'd say that clover is good, but you'll get more use if you establish a perennial plot of multiple species. Similar to annuals, I think that the more species you have in one spot the more use it'll get. My neighbor planted buckwheat, oats, and soybeans in half acre plots. In August/July the soybeans weren't even the first choice for those deer, it was the buckwheat. Then they ate the seed heads, and then the soys. I was amazed that there were any beans at all!
I would say that it is a pretty valuable source of greens in the spring, and then again in the fall, but I wouldn't say it's the best. Besides corn,alfalfa and beans, I'd say in the summer buckwheat is #1, and oats,rye,peas,brassica#1 for fall.