The best chance of big win is football... this is in my opinion. There might be other games but football seems easier to predict. I have seens several people using double digits to win 6 figures from sports betting with football only. On the other hand, I have not seen that in other events.
soccer I think it's quite easy because we can predict it from the way they play and the number of wins from previous matches, but sometimes I can only guess the winning team, while the match score is very difficult to guess.