A/V isnt really my strongest suit but wouldnt VP9 be somewhat in between these two?
It is similarly old enough (as well as open source) to be considered a ‘you can use this everywhere without needing to worry about compatibility’ while being newer/better than H.264.. if not quite boasting the efficiency of H.265 (HEVC).
Or thats what I think I’ve gathered.
EDIt. Just double checked and H.265 was released in July 2013 and VP9 was June 2013. 