In no particular order:-
I’ll start with what is pretty much a niche addon which is ESPN Player (subscription required and not to be confused with the main ESPN addon),
this is a great for fans of American college sports who live outside the USA, although in my case I’m only a fan of college football so this is soon to be retired for me until next September, but it offers bitrates far in excess of what’s available on the ESPN Player website giving a great broadcast quality HD viewing experience.
Next I use the Apple iTunes Podcast addon a lot to listen to my favourite podcasts without the need of having an Apple ID or account.
The YouTube addon also gets used a lot in my humble abode but not in the way most people would use it, its sole use here is for watching trailers for the many movies in my local library.
Back on the sporting front I also use the Eurosport Player addon which is much better than viewing through the website or the Fire TV app as it gives streams in 720P at 50 fps rather than the 25 fps on offer the last time I used the other methods.
Last but definitely not least is IplayerWWW which must be my most used addon, I far prefer using this addon for watching or listening to BBC content than the homogenised way Iplayer content is served up on every other device known to mankind lol.
I used to use the NFL Gamepass addon a lot but sadly it hasn’t been updated for a while and now fails to work so I’m forced to use the Fire TV app which is a goodish substitute.