I would recommend manual because the light is not going to change that much outdoors, once you have the exposure right.
If you want, set your mode according to the way the sun and clouds is behaving. If the sun disappears and appears behind clouds regularly then go aperture. Otherwise if it is a clear sky OR completely cloudy then go manual, preset the aperture to F/8 and ride the shutter speed, only when you need to.
F/8 to F/11 is the best range for the lens, don't need anything smaller for DOF and the image quality degrades due to lens diffraction.
Only time you will need to change shutter speed is when you go from a dark area (woods) to a light area, or vice-versa.