What is the chemistry behind cleaning silverware with aluminium foil
Is any one of these reaction more "true" (occurring more often naturally) than the others or is it the case that a little bit of everything is happening?


I think the best answer is "a little bit of everything".  Silver sulfide forms faster but requires exposure of the silver to sulfur-containing materials (like human skin, food, etc.).  Silver that isn't exposed to sulfur would still be oxidized by the air, but at slower rates.  So depending on the life history of the silver object in question, different amounts of the sulfide and oxide could be present.