William Howes was aksed this same question and I think did an excellent job of answering.
"OK youve asked the question of the century. All the marketing hype in the media has everyone wondering what to do.
First if you have a brand new engine, run the current installed oil for at least 3000 to 4000 miles. This will "Set" your engine components. (Not! break in, bad word)Currently in the petroleum business there are different groups of oils I, II, III, IV, V, VI. Group I is old hat, stuff used in the 50's and back. They are not really avilable anymore to the general public. Group II is still around but being replaced by III and IV. What all this stuff means is that The currently available "Premium motor oils" are at least group III "Highly refined". These are last years media promoted "Synthetics". They are still petroleum products, but are so highly refined that they protect your engine to a point that unless you need "Extended Drain" (15,000 miles or more between oil changes, WITH OIL ANALYSIS!) you are fine useing them. Groups IV and up are "True" synthetics. Manufactured from all kinds of Hydrocarbon molecules that I won't go into. The reason for these "New" products is mainly the requirement of major fleets that want extended drain intervals utilizing oil analysis programs. Some of our (Texaco) products have actually gone 1 Million miles with proper maintenance. You don't need that. So, rathter than buy a Full synthetic at around 20.00 per gallon and changing it out in 3000 miles. Use a premium grade of oil (Major Brand Name) and follow the usual drain interval recommended by your engine manufacturer.
As to protection of your engine, with the type of driving and drain interval you probably follow. The added protection of longterm Anti-Oxidation, Extreme low temperature, extended drain characteristics of the group IV and up is not needed. The protection af a major branded oil should be fine for your new engine. If you do use a full synthetic, remember, change your OIL FILTER at the recommended mileage, top off your oil when you do, run at least on full oil change of Synthetic thru your engine as a flush to get out the old oil, "Set" your engine first by putting at least 3000 miles on it. I recommend Texaco Havoline or Mobil I "Full Synthetics". Do not use a "Semi-Synthetic" just a waste of money.
Hope this helps.
By the way, I sell this stuff and I don't use a full synthetic. "