There is no definitive answer to this question as it depends on a number of factors, including personal preferences and opinions. However, some sports are generally considered to be more difficult to bet on than others.
Some of the most popular sports in the world, such as football (soccer), basketball, and baseball, are also some of the hardest to bet on from a financial perspective. These sports tend to have a lot of variables that can affect the outcome of a game or match, making it difficult to predict who will win. This can lead to losses for those who don't carefully consider all the factors at play before placing their bets.
Other sports that are often considered hard to bet on include tennis and golf. These individual-based sports can be very unpredictable, with even the best players in the world losing matches they were expected to win. This makes it difficult for even experienced bettors to make money consistently from betting on these sports.
In general, any sport that is relatively unpredictable and has a lot of different variables at play is going to be considered hard to bet on by many people. This is because there is simply more risk involved in placing bets on these types of events.