I'm not sure AV vs AR would be, as torino10154 says in the comment above - a fair fight. I think you either love or hate AR - so this might skew the voting.
I like the idea of anon posting, because it puts newbies to the fandom on the same footing as BNFs when it comes to the attention the fic/art gets. But on the other hand, if I read a story I like, it's good to know who the author is so I can read more of their stuff before I get overwhelmed by fest-fic and forget.
I think limits put a crimp on creativity... I see the point, but if I have a prompt I want to go with it as far as it takes me. That might be 5K or it might be 25K. If there's a limit then the fic would suffer, I think.
I love the idea of author/artist collaboration - although I think it might prove a little tricky in practice, speaking as a writer who always sails close to the wind when it comes to deadlines, and I'm sure I'm not the only one...
(Am new-ish to H/S although not to fandom, and am looking forward to the next games!)