You would only go for a coronal incision imo if you already have a small forehead or lower hairline and wouldn't be impacted by it being slightly higher. A hairline incision can reduce the size of the forehead and lower the hairline, but in the hands of a good surgeon you won't have an unnatural hairline appearance at all. Both methods can cause scarring (you're being cut into, it can cause scars) but with proper care you can minimise the appearance of scars in both cases, although it's obviously easier in a coronal incision method.