If you listen to most of the members here, they'll say XenForo.
Using a paid software "because you can" is stupid, especially if you can't be completely sure the site is going to take off. I would start with an Open Source solution, and migrate later. Cost vs. Member etc.
I'm always in favor of getting on board with XenForo, especially with V2 being on its way. #TeamXenForo
As far as sports forum go, it seems like vBulletin is typically what you see them using. At one point in time, vBulletin had a bunch of great add-ons that were specifically geared towards sports forums, so I do know a lot of sports forum owners that are still on vBulletin because of this. One example would be the vBookie add-on, which is a betting add-on for vBulletin. I know that was all the rage on sports forums a few years ago, but I'm not entirely sure it's still a thing.
Both of these add-ons have been around since 2012, and they have both had updates made in the last few months. Given that the developers have shown consistency with these add-ons, I'd say we can assume that these will eventually be updated to V2.