A bit of both! A lot of my pieces are written with a particular submission call in mind; if they don't make the cut at that venue, then I'll go on to submit them elsewhere. But others are written without a specific prompt or call, and for those I look around for somewhere that might like them. What I don't do is simultaneous submissions; I'd rather be patient than find myself having to deal with the admin of sending a dozen withdrawal letters every time I get an acceptance, lol.