In My Kitchen: A Cookbook [Index]
Onions are an amazing ingredient, equally capable of being spicy, savory, or sweet; I use them in more dishes than any other ingredient.
I generally cook with large yellow Spanish onions, at least in part because I find it easier to chop one large onion than three small ones.
Purple onions are particularly sweet even without extensive cooking, and are good choices for fresh tomato sauces, pizza toppings, mexican stir-fry, and other fast-cooking dishes. (And I would only use purple onions to slice uncooked into a salad.)