Grain crops fall into two broad categories....the summer growers, which need warmth and summer moisture (corn, sorghums and millets, and rice); and the winter growers (at least in climates where winters are moderate), which grow in cool weather and need winter and spring moisture (the "small" grains...wheat, rye, oats, barley).
Corn is by a good margin the highest yielder per area, provided
water, warmth, and nutrients (it is nitrogen-hungry, especially) are adequate. It is, as you have surmised already, the easiest to process for eating. There are some corns for dry use (the short "strawberry" popcorn comes to mind) that can mature in only 90-100 days.
In my Mediterranean climate I'm becoming more enamored of the small grains....wheat and barley so far. They need a lot less water and that's the limiting resource for me. They don't yield as much, they are itchy and "dithery" to work with, and take several steps of processing before eating. Wheat is even more versatile in the kitchen than corn is, and barley (besides fueling my fantasy of homemade beer---for which I need to get some hops started too!) makes an acceptable substitute for rice as a boiled grain. Barley needs even less water than wheat does and matures faster....but each grain is in its own little husk, unlike wheat and similar to rice....this must be "polished" off before use. A heavy blender (like a Vita-Mix) does a good job of it at a medium speed, followed by winnowing......