Let's assume secondary professions are included here. The fun option, in my opinion, would be archaeology. You'd still get to explore the world and have adventures! Realistically, though, I don't think I would mind being a full-time chef. Within the rules of Warcraft, cooks gather most of their own ingredients. As a player, I like killing things. In real life, I love gardening. Skilled cooking requires both, so why not be a chef? I even briefly considered attending culinary school. In Azeroth, maybe I'd do it.
What about you? Maybe you'd be a full-time angler. Heck, El already does it.