Added my vote and could see already that Football/Soccer events are the favourite (no surprise there). I don't honestly spend much time on tennis, MMA, boxing or motorsports but I do tend to watch the bigger tournaments so basically will join any competition that involves a certain degree of unpredictability. I can't say I'd participate in NFL or MLB though, since I don't even understand the rules!
Events wise, good enough to hold simple prediction competitions - correct scores, or outright winners are fine enough. But it would be nice to spice up some of the events. For example, if you hold a league contest, in addition to predicting scores, you could also pick a team to support the entire competition. And pick 3 players to support. For each win the team gets, you get extra points. For each goal player you pick scores, or each save, or each intercept (depending on position), you get bonus points.
I know it makes things complicated but you'd be surprised by how fanatic fans get drawn to these added layers of complexity!
Great detailed input! It was definitely not a mistake asking here. We are taking notes of all your suggestion and appreciate it! (And yes, looks like soccer/football is going to be the runaway winner if the current poll trend continues.)