Riding position on a bike has to be a compromise between comfort and efficiency. Too upright, and you are very slow, which will make your commute tiresome and frustrating. Too low, and your neck and shoulders will get sore. A commuter bike should have the handlebars at about the same height as the seat, so your back is slanted forward at about 45 degrees. That way you can keep your head down a bit for reduced air resistance and slightly better speed, but still comfortably see where you are going.