We freely admit that our business involves producing and selling plywood siding and not shingles, so we do have a bias! However here are some honest things to consider.
Shingles used on side walls often look great when they are first installed. They are bright clean and really stand out. But like anything that has a natural finish, they will not stay looking that way. Eventually they will weather and become a very plain looking grayish color.
There are some other important issues to consider. For shingles to keep their bright clean color they must have a high degree of maintenance. Most homeowners end up giving up the battle and dark, drab color wins in the end.
Shingles are very difficult to paint and therefore once they are applied the home loses its distinct appearance. Plywood siding offers excellent opportunity for the use of color to create or maintain the individuality of your home. You give this up when you apply shingles.
Most homes were designed with the exterior original siding intended to complement the appearance of the home. When a home that is originally designed with clean modern lines has wood shingles applied to it, the result is often less than desirable.
Finally, in many cases the installation of plywood siding may actually be must less expensive than shingles. If you are considering replacing your pre-existing siding with shingles because of dry rot, don't make the mistake of simply covering over the rotten material with shingles! This is only a temporary solution. Rot does not go away on its own and can cause major problems later. You must have a good solid substrate in which to nail the singles. Once a cost consideration is made to remove the old siding, and then add new plywood with the new shingles then applied, labor costs can sky rocket!
Whatever decision you eventually make, we encourage you to think through these issues carefully. Once you apply shingles their final appearance will be with your home a very long time.