Have you grown Utah Yellow Sweet Spanish onions? Local stores like to sell Yellow Granex seed here even though the daylength is wrong. They did have seed for the Utahs but no Walla Walla, so that's what I'm trying.
I especially like you to differentiated between planing onion seeds and onion sets and transplants. You will indeed get bigger bulbs by planting the latter two rather than the former......at least I do, anyway .