When I attended cooking school in Paris, I was taught to cook with unsalted butter. In my travels on the world’s barbecue trail, I’ve seen grill jockeys reach for both salted and unsalted.
Salted butter adds a bit more flavor when brushed on grilled vegetables or seafood, but unsalted butter will give you a fine taste, too. The difference isn’t worth making a run to the grocery store. For most recipes use whatever type of butter you have in your refrigerator. However, if a recipe specifically calls for salted butter, try to use it.