I pioneer in northern urban permaculture. Although the are many things arguably higher in production per area, annual grains still fill a niche and I therefore experiment with them. My goals are high production and easy. Here's my analysis thus far:
Wheat: Wheat is a challenge at seed. Things like to eat it, and they recognize it. That said, it's one of the few things that grows over winter, so it's worth a try. Sprouting and deep seeding or covering is pretty much the only way it won't get eaten here. Same thing at maturity. Harvest early and dry inside. Processing though is fairly easy and production per acre is not all that bad. However, it does produce all at once and only produces if it's planted at the right time. It also has no great secondary edible value. You either win or loose. I believe the estimate is somewhere around 1 cup of flour per 20 sqft. It is, however one of the few rising grains. This is my winter bed filler. Anything that doesn't get greens, carrots, or edible aliums ends up in wheat.
Sorghum: Sorghum has high production per acre, repeated production, and a secondary crop (molasses). It grows fast, germinates readily, and can be planted any time where you are frost free for 2 months. It produces even if you only get one plant to grow. I haven't had as bad predation issues. It has a tertiary crop of dried flowers. Processing is fairly easy too. Pet the seeds out, grind them. I have gotten about 2 cups seed per 20 sqft, planted spring to fall. I usually plant this out to a bed because of its high production and low maintenance, but because of its aggressiveness I have to watch it doesn't shade out other things.
Buckwheat: Here in a wet climate buckwheat falls over, then the seeds either resprout or get eaten. If you don't mind leaving on the hulls, processing is fast. Theoretically it would have high production and the flowers are noteworthy, so I am attempting to breed a better buckwheat for here from plants that went rogue. One plant can produce 2T of flour here. So theoretically I could produce well over 2 cups per 20 sqft.
Millet: Millet is another tough starter because it turns out ants and everything else eat the seed as soon as it hits the ground or sprouts from a mature plant. I did fight my way to a handful of seed for next year. It grows fast and can with stand hot and dry very well. I like this for a fastsummer filler crop that may not need to be showy.
Corn: Corn needs close friends and lots of them to produce. There is disease associated with corn. The stems are a secondary crop as a sweetener. Tertiary crop is the decorative dry corn and stalks. Production is about 1.25 cups seed per 20 sqft. Processing is fairly easy. I do have to compete with the squirrels, but they are mostly after the sweet stems. Also, many of the corn varieties I bought had weak stems and flopped over. I've had to breed a stronger stemmed variety. I'm now working on increasing its productivity. Theoretically I should be getting double the production. I usually plant this to a bed because corn is such a desired grain here with a theoretical triple production to wheat.
Sunflower: Sunflower is delicious to wildlife and they recognize the plant from afar. If you can fight them off it's a delicious grain and the larger varieties provide nice trellising for other crops. They are very eye catching and some varieties are multistemmed. And, the buds and sprouts are edible too. This is a good filler for a late spring summer bed, or really anywhere you may need to stake some late climbers.
Amaranth: Beautiful, easy to process, nutritious, fast growing, can be planted late, doesn't need large quantities to produce. I estimate about 1 cup seed per 20 sqft, but the grains are so small that it's a dense cup! Wildlife don't seem to recognize it or atleast don't dessimate it the way they do other crops (so far). You can also use them as greens or sprouts, if you want. This is a great filler in any area where you need a plant that can sprout in the heat and dry of summer, and impress the neighbors.
Quinoa: Quinoa can be pretty, hardy, and is fast growing, but in this climate it's a little tricky. Any moisture on the plants will start the quinoa sprouting before you get to harvest it. However, like amaranth, the wildlife don't gobble it up super fast. It looks exactly like lambs' quarter until it produces a seed head. Then some varieties can be quite showy. It's also one of those with edible leaves, so over-seeding or sprouting provides an additional crop. I have yet to achieve a fully mature quinoa stand because I have put them in harsh sight conditions. However, unlike amaranth and sorghum, when it seeds, it dies. Theoretically, if I extrapolate from what I've seen, they could produce about 1 cup seed per 20 sqft. This is a good late spring crop or really any frost free time crop where you need something to be quick, but are sick of radishes and arugula.
Barely: A lot like wheat, except you need to spring plant it here and it matures about 3 weeks before wheat. The down side is hulling is pretty much impossible and the flavor is cardboardish. It's traditionally called an animal feed. This is my back-up for failed wheat beds and other early spring crops.
I still haven't explored hulless oats. What other annual grains are out there that I'm missing?