The Mitch Rapp novels are generally numbered in the order of their publication. For example, 'Transfer of Power' was one of the early ones. However, it's best to check the official Vince Flynn website or a major book retailer's listing for the exact order as there are quite a few in the series.
Personally, I think starting with 'Transfer of Power' is a good choice. It gives you a great introduction to Mitch Rapp and his world. Then you can move on to 'The Third Option' which further develops his character. After that, continue with the rest in the order they were published as each book builds on the previous one in terms of plot and character growth. For example, as you progress through the series, you'll see how Rapp's relationships evolve and how his skills are tested in different scenarios.
One of the highly regarded Mitch Rapp novels is 'American Assassin'. It delves into Rapp's origin story, showing how he becomes the lethal operative. Another great one is 'Kill Shot' which features intense action and Rapp's signature brand of counter - terrorism. 'The Survivor' is also a must - read as it continues to develop Rapp's character and his fight against global threats.
Mitch Rapp novels are the creation of Vince Flynn. His writing style and the compelling storylines in these novels have made them a favorite among many.