Desktop. I think most creators will give the answer of desktop or laptop because the mobile app isn't made for us. It's made for the readers on Tapastic. Creators can't check our notifications or create comic posts very easily on the apps so it's very limiting that way.
When I am on the go, I do use my smartphone but I don't use the Tapastic app. I open the full website on my phone. It's a bit of a pain but it's semi functional for on the on use.