With sports betting, the odds only differ depending on the players/teams in the competition. For example, in Aussie Rules Football, if the best team in the league were playing an average side, they are always going to be odds on to win. However, if the best team in the league were playing the second best team in the league, they might still be favourites but the odds might be closer or the second best team in the league might be the favourites depending on their current form/results.
In sports such as Golf or Tennis, the players who are ranked the highest in the world rankings are usually always going to be favourites against players who are below them in the rankings. Therefore, the odds compare in sport to sport by the current rankings of players, the current form they are in and the format of the specific competition.