There is no simple answer to this question as it depends on a variety of factors, such as the type of business, the products or services offered, the business model, the target market, the competition, the industry, and the geographical location. Furthermore, what may be considered the best startup in the world for one person may not be the best for another person.
That being said, there are a number of ways to measure the success of a startup, such as revenue, growth, profitability, market share, and so on. Depending on which of these factors is most important to you, you may have a different opinion on which startup is the best in the world.
Some of the most successful startups in recent years include companies such as Airbnb, Uber, and Google. These startups have disrupted their respective industries and have become household names.