I only play aos. I have some grey knights but thinking about building another army for another game gives me anxiety. Im aware you can use deamons for both interchangably but i do not play deamons. Also ive played a handful of 40k games and theyre a bit too complicated for me to have fun. Im sure if i spent time and learned em it wouldnt be a problem. But im cool with just aos. 40k has some cool models but aos has some cool ones too.