In my opinion, the greatest value of compost is its effect on soil structure and performance. I use whatever I have for the compost because I don't send any organics to the dump. A wider variety of ingredients may tend to provide a wider variety of nutrients in the final product.
Renais

There will be some differences. Compost can be thought of as a combination of 1) organic matter, or humus, which is the majority of it; 2) major nutrients like NPK; and 3) trace minerals such as Fe, Mg, Ca etc.

Generally speaking, humus is humus, and different types of ingredients make similar compost. There are exceptions such as slow-cooked leaf compost (leaf mould) but for the most part it's pretty similar.

Major nutrients can vary depending on the inputs. A mostly manure compost might have higher levels of P than a compost made from garden trimmings. Most compost is in the range of 0.5 to 1.5% each of N, P and K.

Micronutrients can vary quite a bit as well. I tested about 20 commercial composts plus my own home made compost, and found that some had plenty of one mineral or another but were low in others, whereas some were very well balanced. It's said manures can be a bit 'salty' if they come from feedlots.

If you're adding plenty of compost to your soil and using all the compostables available, generally your soil will be fine. There is hardly such a thing as completely useless compost.
Bottom line: Adding compost vs. not adding it has a far greater effect on soil health than what kind of compost you use.

The greater the variety of material that is used to make compost the better the finished product will be.

I've been wondering.....if I only feed my indoor worm farm buddies coconut coir and shredded paper, are the resulting castings less 'fertile' than if I feed them baked sweet potatoes and banana peels? That makes sense to me but not sure if it's true. What think y'all?

during the last growing season, I used straw to put down under all the plants, as to save water. I am in northern California. we are in a severe drought. before the rain I have planted some fava beans. the fava beans are grown to a state that I want to cut them down. If I cut them down and keep them on top of the straw will the cause to much density or will I help the soil? sorry for the long drawn out version

Mary, paper has little, if any, nutrients. Most everything
I have seen about Coir is that, like peat moss, nutrients need to be added since Coir has very little as well.

Wolfman, cutting the fava beans and laying them on top of that straw would be a good idea since those stalks would give the Soil Food Web a food source. Straw is essentially cellulose with little nutrient value.

Thanks kimmsr, just what I thought, appreciate the confirmation.

I've had bins that were close to 100% dead leaves, chipped branches and pine needles: they composted just fine because I kept them moist.

It's partly the speed and ease of composting.

Grass-only compost easily packs down, then goes anaerobic and stinky because the fine strands pack down. Grass and leaves composting - layered or mixed before adding - goes faster because the leaves keep the texture open for air.

Leaves and food scraps ... depends on the food scraps.

Leaves and manure - if there's livestock urine mixed with the manure, tends to compost fast and hot ...

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In short, most of us use what we can scrounge, rake or get from the kitchen.

My current heaps are just the weeds and leaves from the yard cleanup here, layered with kitchen scraps and coffee grounds, and used cat litter sawdust (minus feces). I'll see what the middles look like in a couple of months when I get serious about the garden beds and break them down.

Compost's primary function in my garden is as a supply of organic matter to improve soil moisture-holding capacity, lighten up heavy clay soil, make sand hold some moisture, and as a top layer to retain moisture. I'm unconcerned about nutrients.

SPOILER ALERT!!!!!

KIMMSR DO NOT READ!!!!

TRIGGER WARNING!!!!!
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(If I'm worried about nutrients, I add fertilizer from bags, in very small quantities)

I read a study on this. Unfortunately it was from Malaysia, so the candidates were two kinds of rice straw and sawdust. The sawdust was best. I don't know if we can generalize that harder to compost things are better. Sad fact is most of us don't have much choice if we are composting in any quantity.

lazygardens, if you are concerned about nutrient levels have a good reliable soil test done. Never simply throw some "fertilizer" onto garden soil because unbalanced nutrient levels can create more problems then they will ever cure.

Well, that didn't work, but at least things are predictable around here. :-D

@kokopelli: What criteria were used to determine which compost was "best"? NPK, micronutrients, health of plants grown in it,...?

I would think somewhere there are published studies on nutrients and performance for different kinds of compost. Seems like that would have been done years ago.

They used plant growth, in this case maize. Chemically, the sawdust had higher humic acid, but others had higher nitrogen.

Thanks, that makes sense.

What a great question. I have made custom compost in the past.

Some batches featured more wood chips and shredded pine needles and this went under the raspberries.

I have make compost from 100% shredded oak leaves and after hot composting in a windrow, I moved it into a compost bin. Once it cooled enough, the red wigglers moved in. By now that stuff must be nearly pure worm castings, and would be fantastic vegetable garden compost.

Straight ramial mulch, made from fresh green branches run through a chipper, was a very hot compost - almost as hot as a grass-clipping compost. I used that as a mulch around young trees.

But most of my compost has been the generic greens/browns mix of leaves, grass and kitchen waste.