Another interesting thing to mention, is the type of onions that chefs seem to prefer, which seem contradicting. For example:
Bruce Edwards: Suggests spanish onions as being the best.
Julian Voigt: Suggests Dutch or English.
Someone else I read today (and can't seem to find again) was suggesting english onions _only_. This obviously doesn't give a very good sense of clarity over which type of onions produce the best results, if there is a huge difference between them.