Sally does all of her wire-frame mock-ups low-fi, while Cindy does her mock-ups in Photoshop. It doesn’t really matter which method you use. It really comes down to the finished product and what the client asks for. Sometimes it’s much faster to do the majority in low-fi and then translate it into high-fi, but for others it’s faster to start in Photoshop.
So the answer is? It’s defendant on what you are comfortable with and can budget for.