Great question and the answer is you can use either, as they are very similar! While both cuts contain the name sirloin, they are in fact different. Top sirloin is a bit more tender and comes in smaller size steaks that are great for grilling and also cutting into cubes to stir fry. Top sirloin tends to be a bit pricier as well. Sirloin tip on the other hand is a bit tougher, but don't worry, it is still tender. It is often sold in roast size cuts and is a bit more economical. Either works for this recipe.