I have been growing onions for many years from seed and sets... I prefer seed grow. However if you were new to growing them and were looking for advice on the net... what confusion would you meet. I was trying to get a definitive on the subject of ground preparation so did a google search. Below are two of the results one exactly below the other on the list.
old farmers almanac says
Soil needs to be well-drained, loose, and rich in nitrogen; compacted, rocky, or clay-heavy soil affects bulb development. Add aged manure or compost to the soil in early spring, before planting. Onion plants are heavy feeders and need constant nourishment to produce big bulbs.
BBC says
A sunny, well-drained site is essential for growing good crops of onion and garlic. ... Onions and garlic both like fertile soil, but neither require much nitrogen and so shouldn't be grown on freshly manured soil. Instead, dig over and manure the ground several months before planting.
So the take home message here is? One other interesting feature was that both recommended growing from sets for ease and reliability of product, personally I have found that seed grow onions are much better and rarely if ever go to seed whereas I have had loads of bolted onions from sets one reason why I stopped using them??