Wikipedia:

[edit] Synthetic Base Stocks
Synthetic motor oils have been made from the following classes of lubricants:

Polyalphaolefin (PAO) = American Petroleum Institute (API) Group IV base oil
Synthetic esters, etc = API Group V base oils (non-PAO synthetics, including diesters, polyolesters, alklylated napthlenes, alkyklated benzenes, etc.)
Hydrocracked/Hydroisomerized = API Group III base oils. Chevron, Shell, and other petrochemical companies developed processes involving catalytic conversion of feed stocks under pressure in the presence of hydrogen into high quality mineral lubricating oil. In 2005 production of GTL (Gas-to-liquid) Group III base stocks began. The best of these perform much like polyalphaolefin. Group III base stocks are considered synthetic motor oil in North America.[2]

Now, depending on your situation, describe "better". Warm climate with extended run periods and you likely won't see much of a difference. Cool climate with short run periods and the "synthetic" will usually win out due to its flow characteristics. All in all, there is no magic oil, regardless of what that mechanic tells you.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )