I would say navy. Charcoal is a fine suit, but navy will serve you better. Make it as simple as possible. No details like ticket pockets, peak lapels, or odd button stitching. Go with a simple two or three button (I prefer two), the best fit you can get (don't be afraid of an alterations tailor) and the best quality cloth you can afford. Then start saving for a good pair of shoes. Since you've got a black suit, and navy can get away with black shoes go for those.