What is the most profitable franchise to purchase?

I'm curious to know, when it comes to franchise opportunities, which one stands out as the most profitable to invest in? Could you elaborate on the key factors that contribute to its profitability, such as the industry it's in, its market demand, and the potential for growth and scalability? Also, what are some of the challenges or risks associated with this particular franchise, and how can potential franchisees mitigate them to ensure success?