Here are the most profitable sports when betting against the spread:

College Football (97.83% OPT. ROI SCORE)
NFL (90.2% OPT. ROI SCORE)
College Basketball (36.91% OPT. ROI SCORE)
NHL (12.39% OPT. ROI SCORE)
NBA (10.33% OPT. ROI SCORE)
MLB (8.81% OPT. ROI SCORE)
Odds are presented as a positive or negative number next to the team's name. A negative number means the team is favored to win, while a positive number indicates that they are the underdog.