I used to think Soccor (futbol) was boring but now I enjoy watching (still not as much as American Football even though there is only 11 minutes of play time as anticipation heightens excitement).
I used to like watching baseball but now I think it is the most boring to watch. Being at an actual game is fun, but that is because I enjoy things like buying snacks from vendors, people watching, doing the wave, and betting on whether the catcher throws the ball on the mound at the end of an inning more than the actual game, so minor league $3 ticket games are just as entertaining as major league $30+ ticket games, but watching a game on TV is more boring to me than watching a live fishing or hunting show unedited (where they catch something every couple hours and sit there the rest of the time).
For most entertaining, I would vote X-games style such as Skateboarding, BMX, Blading, Motocross, Waveboarding, Snowboarding, etc.