I think that one of the best food smells--excuse me, perhaps I should say, "One of the best aromas resulting from the application of heat to edible plants or meat"--is the scent of garlic and onions sauteing in olive oil.
Another would be rosemary on broiled chicken and/or potatoes.
In the top five food smells is this one:
The scent of ripening nectarines (or peaches).
These lovely fruits are sitting in my kitchen area, driving me crazy--they aren't ripe enough to eat yet, but they smell wonderful (perhaps because I keep sticking my nose amidst them).