I use Sling, at least during college football season. There have been lots of threads about this. It depends entirely on what sport you want to watch, and whether you follow the local teams or out of market teams.
Basically, in order of ease of watching without cable:
NFL - Most local and big time games are on free tv, exception being MNF which is on sling. Sling also comes with access to WatchESPN, which can stream content on-demand(but only from ESPN, ESPN2, and ESPN3, not from the other ESPN channels).
NCAAF - Lots of good games on free tv, and even more on ESPN via sling. You do miss out on some games, but you should rethink your life if you are watching that much football.
MLB - MLB.TV is by far the best sports app. Its ~$25 per month for 6 months. You can watch games live or on-demand via roku, apple tv, fire tv, etc... If you want to watch the local team, you will need to do some shenanigans to fool the app into thinking you are out of market. This is not too difficult, but does require some technical skills.
NBA League Pass - Its like $50 a month for the season for all games(minus local broadcasts), or like $35 for one team(not the local team). If you want to watch the local team, its more difficult than MLB, but it can be done. Sling TV does have ESPN and TNT, which will show 500 Lakers games plus a few others...
NHL/Bull Riding/Golf/Tennis/Whatever - No idea, since I don't watch or follow these.