Been trying my hand at farming on my current URW game, and decided to share my thoughts on each plantable crop. As a minor disclaimer, I am using BAC crafting mod, so I have access to a few recipes that allow more efficient usage of flour than vanilla's flatbread and porridge. Also, some more variety in how to prepare everything else too, but that's less important. More importantly though is that it allows me to turn yarn into cloth and from there into actual clothing, thus giving more reason for more extensive planting and harvesting of textile plants.
Barley: Great nutrition. Takes a pretty long time to grow, but generally can grow to maturity when planted planting as soon as it's possible on spring unless you are too far north, and it can have quite large stacks of plants per square, which means you can either prepare less soil or use more soil for everything else. Harvest window is pretty narrow though, so people just dabbling in agriculture will likely have trouble.
Rye: Nearly functionally identical to Barley, except a bit little worse. Very slightly less nutrition, takes slightly longer to grow. You might want to plant it in fall instead to winter the crop and see it sprout earlier next spring, specially if you are not really to the south. Very narrow harvest window, specially if planted on spring instead of wintered. I somewhat Rye flatbread in specific being used in some ritual, but my current characters don't have that one so I can't confirm. It might be easier to just trade for some bags of Rye instead if that's the case though.
Turnip: Relatively low nutrition for its weight, but very heavy. Grows really fast, and if you can often get two harvests per year if your timing is good. Great filler for when you are already on abundant nutrition, or if you really need something to help you last until the better crops are ready for harvest. Do seem to bring pretty large stacks of crops per square. Seems to work as bait for Elks and Reindeers in traps. Seeds not worth trying to make into food though, unless you are desperate.
Broad Bean: While not the most nutritious per weight, it's more than enough to keep you very healthy. Takes relatively long to grow, but has a very large harvest window, only withering a month after winter already started. Good if you are only dabbling in agriculture and/or like to travel and might miss a narrow harvest window. Not very large crop stack per square, but each plant does get threshed into five large bean pods, so it's remains a solid option. Worth mentioning that 3 broad bean pods will just exactly fill the meat soup requirement for vegetables (and the meat stew option for it) without any leftover.
Pea: Low nutrition, takes pretty long to mature, small plant stacks, only produces 2 small pea pods per plant. Honestly, rather useless to plant. Harvest them if you find them on the wild, sure, and you can always try to trade for it (although villages seem to only have half bags of it for sale, but that's just a matter of consolidating them in a single bag later). Honestly, I don't know why you'd plant this unless it's for roleplay purposes.
Hemp: Very versatile. Textile crop, making one fibre per about 8 dried retted straw/plant. Each plant also produces 2 fistful of seeds, at about 100g each, with pretty good nutrition, in addition to 2 fistful of leafs (with pretty low nutrition due to thresh multiplier, but not quite insignificant), at about 2/3 of the weight of the seeds. Takes very long to grow, and depending on where your farm is, they might wither before maturing unless you winter them. Like all other textile crops, can be harvested early just for fibre, but that's something of a waste given how good they are for food. Relatively small stacks. Also [insert jokes about weed/police attention/420/whatever here].
Flax: Very good for textile, at 1 fibre per 5 straw/plant, matures pretty quickly and survives quite a bit of time. Flowers before full maturity, which might be worth if you want to brew some flax tea or something. Fully mature plants produce 2 seeds per, at about 10g per seed. Quite nutritious, but simply not enough weight to live off it unless you really go out of your way to make massive flax farms and take a massive time threshing everything. I generally find it worth planting to make textiles, with the food as a nice bonus out of it.
Nettle: Textile, at 1 fibre per 15 straw/plant. Plant produces leafs and seeds, with seeds barely more nutritious than turnip by weight, and leaf insignificant other than the medicinal properties. After you get a bit of a leaf stockpile to use for their properties or as seasoning filler, might be worth to just harvest young instead of waiting for maturity. Honestly not worth planting. It does have one big advantage though, in that it's incredibly common in the wild, specially on river and lake banks. Just take a boat trip and can get massive quantities of it very easily.
Clayweed: Nutrition is pretty good, but stacks are pretty small, and each plant doesn't produce much. Definitely better than peas, but then again, just about everything is. There are better crops, but might be worth for a challenge and/or roleplay. But honestly, just harvest it on the wild.
Yarrow: Useless nutritionally. Somewhat common on the wild. Pretty good set of medical properties. Get a stockpile of it, ideally from the wild unless running a challenge or have roleplay reasons for not doing so, and there you have it.
Sorrel: Useless nutritionally. Incredibly common in the wild. Pretty meh set of medical properties, but not entirely so. I wouldn't even bother harvesting it unless I'm desperate or just want some to stockpile to roleplay more variety in food.
And as a bonus,
Lake Reed: Not plantable, but massively common across most lakes. Very good nutrition, with a root that can be used as a vegetable or ground into flour. Takes a bit of time to actually harvest, at 4 minutes per plant, and it comes in somewhat large stacks in very large clusters of plants. Take a week or two to go on a boat trip and come back when your punt is basically overloaded with them. Might have to make a few shelters around the lakes, because they mature around a very wet season, which makes just sleeping on the boat a bit annoying. And with the harvest time, you'll very much have to sleep during such expedition. 3 roots per plant, with each root about 50g.
Milkweed: Surprisingly decent nutrition on the root, pretty solid set of medical properties. Quite common in the wild. 4 minutes per plant to harvest. Wouldn't consider depending on it for long term survival, but it's pretty good forage during long trips and expeditions if you brought a pot.