Exterior paint selecting is easy.
How soon do you want to re-paint?
If you are going to be there a long time, and are not going to change the color, get the higher grades.
Duration or Emerald are both great. The difference is Duration goes on thick and can be harder to use, especially when it is hotter outside. Emerald goes on easier, more like the Superpaint.
***Make sure to use a high quality caulk as well, probably around $3-$4 per tube. Most likely the caulk you use will crack out and fail causing the need to repaint before the paint needs recoating.