synthetic oil?

When I took my top end off on my motor while running synthetic oil, this is what I found. This is what my pistons looked like at the moment of head removal.

This motor had about 22K miles on it during tare-down.

This is what they looked like when I just wiped them with a dry rag.

This is what the inside of the combustion chambers looked like after I wiped them with a dry rag.

Here are some pictures of the cam lobes using synthetic.

Here is a different one.

It's really a question of your personal maintenance practices. Synthetics will not break down (lose viscosity) as quickly. If you tend to stretch the time between your oil changes, use a synthetic.
However, loss of viscosity is only part of reason to change your oil. Any oil is going to be contaminated. Rings, bearings, clutch plates and other components all wear regardless of what oil you use. This ends up in your oil. Heat developes acids and cooling causes water condesation. Obviously, the longer you go between changes, the more contaminated your oil will be.
Personnaly, I use non-synthetic. I prefer to pay half as much, but change it twice as often.