a lot depends on where you are and what you can get locally, cheap.
I used to ride, and used old horse-muck in large quantities. The old, rotted, black stuff is best. Wood-shavings bedding does not smell unpleasant like straw bedding does, and is not so wet. It gets very hot while rotting which kills weed seeds and bacteria, provided it has been stacked deep and turned once or twice. You can even use it as a mulch if you like the smell (I do) as it dries out on the surface and suppresses weeds. If you are lucky you will also get slow-worms in it and baler-twine which is useful in the garden. Now I just use garden compost and a little growmore.
Farmers muck is likely to be from cows or chickens, very wet and smelly, and likely to contain a lot of chemicals and strange weed seeds unless it has been stacked for a few years (which is unlikely).
Zoo muck can also be very good and keeps foxes and other animals away.
My old mum's garden is large, and has two substantial compost bins. i turn it over once a year, and use the old stuff for mulching while filling up the other bin. It has a good mixture of lawn mowings and dead leaves (which is better than a single-component heap) with prunings, hedge-clippings and vegetable waste. Garden compost is good for soil condition but low in nutrients. Some councils also sell compost which they have made on a large scale with garden waste they have charged you to take away.
IMO once you have got the ground in good heart, a thick mulch every year is the best thing, it will suppress weeds. look neat, and the worms will take it down and improve the soil for you; next year it will all be gone apart from coarse twiggy stuff and you can apply some more. I don't often dig.