if you mean apps with results, rankings and news, well, I don't use any...I rather go with normal websites.
if you mean apps to watch sport events on TV comfortably lying on the couch, well the list is quite long (normally, I'm using android TV apps and apple tv apps).
I have almost every OTT service you can imagine: MLB.tv (baseball), ESPN Player (NHL hockey, NCAA sports), NFL GamePass, NBA League Pass, Discovery Plus and of course all those free apps where I can find some sport events I'm interested in (from Youtube to the Olympic Channel to most National TV apps -thanks to a good VPN, obviously).
and sometimes I add a few more when it comes to the climax of certain competitions (namely, the Korean and Japanese IPTV service to watch their baseball champs playoffs).
not to mention, 2 or 3 satellite TV subs, too.
I'm a bit sick, I must admit...