Im a die hard yellow onion fan its the cooking technique that makes them sweet from being caramelized it takes forever where I live due to the high elevation no sugar no nothing cook them until they are almost burnt then be sure to deglaze pan as that is where the flavor is, use a really good strong beef stock.Then let it simmer and add white wine or some sherry,a little thyme and salt and pepper to taste and simmer some more.Some times I even take the onion skins and make a stock with those to add to soup.
What it really boils down to is personal preferrence.
I also think its much better the next day. And of course have the best croutons and swiss you can get.I make my own croutons that are soo good.
Also you need a ton of onions as they cook down to nothing they will swell back up after adding to stock but I like lots of onions.
I dont understand why almost every recipe Ive seen says to cook them till golden brown the trick is to cook them till they are sticky and dark brown hence the flavor comes from the really cooking the onions dont be afraid to really cook those onions and cook alot.If you think you made too many save them and put them on a burger or sandwich.Yummy!