This is not to suggest that these foods are always the best nutrition choices, but if fast calories are what you need, fat food will do it fastest. For that answer, look to your toilet-before flushing. Your own best fat level depends on many variables. Well, not usually. The source of calories has nothing to do with their ability to become body fat.
Calories are, in truth, just units of energy.
If you take in too many calories for your daily workload, that energy will probably be deposited on your body as flab fat. So, the source of the calories has little to do with body fat. Fat calories are usually empty. A donut, for example, has as many calories as a chicken breast. Each of these foods contributes calories, which are units of energy.