I would not use either of those two options. Sponges don't pick up dirt, they just wipe it around which will scratch. If I were to use a brush I'd probably go with one made of natural animal hair. Most are about four times the amount of the one above. They are convenient and if I was doing a big truck, trailer, etc.. I'd go that route. But I find they are harder to really get clean and take more care to keep fresh.
A nice microfiber or wool/sheepskin mitt works best. Picks up and pulls the dirt away from the paint, and can be washed out easily to remove all contaminates. microfiber mitts are cheap enough that if you drop it in sand or it starts to get dirty or worn, you can toss and replace for 5-6$. Wool ones cost a bit more but last longer as well.
In the Winter wear a thin fleece glove and put a rubber glove like the ones they sell for washing dishes or for an even thicker larger glove the ones for handling chemicals. Keeps your hands warm and dry.
