to my mind, the most popular sports are football, volleyball, bascketball,golf
but there are a huge variety of sports, you can choose what you like the most
I would replace golf for tennis but it's your opinion. Moreover it doesn't matter whether sport is popular or not. If you know a lot about it, then you will make a lot of money on betting
you're right, you should be aware of it, but the more popular sport is the more money you can get from it