The best sport to bet on for making money isn’t the sport that is easiest to beat. That might sound confusing but once you learn about limits you will know it’s a lot more complicated than sport X have weak odds, therefore, it’s easy.
NFL, for example, is pretty damn difficult sports league to consistently beat because the bookies tend to price the teams accurately however because there is so much liquidity in NFL, meaning a lot of people bet on NLF you can lay very large bets.
So if you can make $100,000 bet with a tiny edge versus a $1,000 bet on with a big edge, what is most profitable?
It gets a little bit complicated to tell which league or sport is easiest to bet on.
Notice I also said, league. For example, a football league(European football) somewhere in the middle of nowhere that nobody has heard about might have very weak betting lines that you can take advantage of but you will only be able to bet peanuts. But the premier league, for example, will be significantly harder to beat but it will be a lot easier to get down big bets as pretty much all bookies offer EPL betting.
In MMA we see this all times with unknown prelim fighters in the UFC or even outside the UFC where the lines are weak but bookies just won’t accept large bets.
For most people reading this, it won’t really matter because casuals or even semi-serious bettors rarely bet so much that bookies will start limiting you. For a professional bettor looking to make a full time living then it’s a serious concern.
So to answer the title in question: It really depends.
My advice is to focus on the one sport you good at and approach it with laser focus. Don’t start jumping to other sports because you think the money is better but you don’t really care for the sport.