Soya protein powder (isolate) has less calories and over twice the protein of soya flour. Examples I found flour is abour 40g protein and 450 Cals per 100g and soya protein powder is about 90g protein and 330 Cals per 100g. So you would need to eat over twice as much and would get fat ! (unless you worked it all off of course)

As escarmalanes wrote isolates have a higher protein content, so if your goal is maximize the protein/calorie ratio a powder is a better choice. Besides a powder is usually more soluble than a flour and have a better taste.

On the other hand protein powders are (highly) processed foods and could have many additives, while the flour is as close as possibile to the original food source, so it's healthier. Besides, as you said, it's cheaper so it usually has a lower cost/protein ratio. The choice is yours.

Lastly if you have to choose just one source I'd highly recommend hemp: hemp protein is complete, it has a very high fiber content and it's difficult to find it and eat it in other forms, while it's easy to eat peas or soy. Variety is good.

I would suggest a mix of protein sources. I typically buy mine from truenutrition.com and make a blend of brown rice protein, hemp protein, pea protein, flavoring, and vitamins. One scoop varies from 21-24 grams of protein depending on how I play with the ratios.

I'm curious about those of you who use protein supplements...

What is your macro-nutrient ratios? Do you try to meet any particular ratio goal?

I find that I can't add protein supplements because I go way over on protein. My goal is 80/10/10.
I sometimes hit 15% protein but I try to stay under 15% for sure; that also goes for fat %, always try to stay below 15%.

I sometimes struggle to get above 50g of protein, so on workout days I add maybe 20-30g more in hemp or peanut or soya protein, just a scoop in my breakfast or a smoothie. Looking through my history the highest I've ever acheived is 90 (I weigh 168 lbs/76kg)

I'm curious about those of you who use protein supplements...

What is your macro-nutrient ratios? Do you try to meet any particular ratio goal?

I find that I can't add protein supplements because I go way over on protein. My goal is 80/10/10.
I sometimes hit 15% protein but I try to stay under 15% for sure; that also goes for fat %, always try to stay below 15%.

There is a minimum amount of protein (and fat) you need to be healthy regardless of what your overall calorie intake is, so ratios aren't necessarily the best way to do it. The minimum RDA of protein for men is 56g (46g for women), but this is low and should be a bare minimum. Older people and active people probably need more than this. You will also see a recommendation of 0.8g/kg of body weight as a minimum protein goal. I aim for a minimum of 1g/kg just to be on the safe side. Is there a reason you don't want to go over 15%?

I know about the minimums, I'm always above the RDA. I still watch my macro ratios, because I find they are a good indicator of whether or not I'm sticking to a low fat, whole foods, plant based diet. The only way to go above these numbers on WFPB is to eat more nuts and seeds. I'm not interested in supplements, including protein powders, yet I'm still curious what it does to people's macros, hence the question.

I do supplement to meet my vitamin D and B12 needs, but that's it, since I don't eat animal products and I live in the northern Rockies.

That's cool, I think the main reason people use protein powder (at least why I do) is the targeted intake of protein without also consuming fat/carbs as you would with most whole foods. Convenience is a factor too.