Predicting a champion in league is completely hard, but usually it's not away from the top 3 favorited teams. But I'd consider to bet on a match, not predicting the champion.
Not only the Champions league, predicting any sports isn't easy at all, because even games with low odds can lose, how many times we have seen our parlay lose by 1 match, it's really common.
Personally, I like to bet in UFC because the fights are fast, you don't need to be waiting a long time to see your bet results, and since it's a 1 vs 1 sport is common to win with the underdogs, you only need to see one good punch to turn the odds in your side.