They both are dual filament, 12V bulbs with 21 and 5 watts. They both fit the same.
Had the running filament burn out on my brake light, and realized there are the two different ones in there. It was the 1157 that had a broken filament.
Ended up buying a 2057 because the that's what the good bulb was.
The only difference I can tell is the price between the two bulbs.