Is it better to use US dollars or dong in Vietnam?

I'm curious, for those traveling to Vietnam, is it more advantageous to use US dollars or dong as the primary currency? Are there any specific benefits or drawbacks to using one over the other? How do the exchange rates compare, and are there any fees associated with converting one currency to the other? Additionally, are there any local businesses or vendors that prefer one currency over the other? I'd appreciate any insights you can provide on this topic.