if you're a fic writer who's heavy on detailed thoughts and narrations of every character and free imaginary visualization, i suggest on ao3! if you prefer editing through different apps & direct visualizations, more likely socmed aus is for you ~ it really depends on how do you want to write your story, and what makes you more inclined on writing it ~ for me, i've been writing socmed aus for two years now (stopped last year hehe) so socmed aus are more comfortable for me to write!