I call it both interchangeably and tag it as both on my blog as well. But I started saying DeanCas when talking in public venues (i.e. twitter) because Destiel got such a bad name and became almost solely associated with porn. And while there’s nothing wrong with writing porn, that’s just not what they were only about for me. They’re about an endless and overcoming love that stretches beyond fate and destiny and heaven and hell and purgatory and even god because no matter what happens, they always find their way back to each other. To me they’re the greatest love story ever told and while sadly sometimes “Destiel” gets a “lolz ships lol gay u go but no homo lol” reaction, when you say “DeanCas” (or Dean and Cas) people know you’re talking about them as characters too and not just a ship to be associated with porn.
Man that was way longer than I thought it would be, and I rambled so I hope it makes sense, nonny.