Irfan for images and vlc for video is the name of the game for me (and total commander for file management, the efficiency compared to simpler stuff is still in wow territory).
IrfanView likely still supports more formats, since it was earlier than any other tool. This means any edge cases in file encoding that might not work, or render ideally likely has been solved there first.
It probably has some batch file conversion tricks in it too.
IrfanView also provided for free for a lot of years what was hard to get without paying. If it existed on mac I'd be all over it.
Ah, the windows viewer always wasn't that good.
And if I remember the big first improvement of it was copying a lot of IrfanView.
Since this post, I remembered another old friend that was excellent on windows, AcdSEE. Also worth looking into.