that a good oil is a fresh oil, speaking generally. All these new oil types claim to have additives to take care of contaminants from engine wear/combustion, to prolong service intervals. And new models have very long service intervals. However, our older cars more quicly contaminate the oil, and we should change often. And then you might opt for a cheaper oil (not a cheap one).

The real reason why you might want to go for a synthetic, and why you were recommended one, is that if you drive up in the mountains or up north in the winter time, temperatures around 0 F might make the oil very "thick" and engine almost impossible to start, unless you have a synthetic or special winter oil. You got good advice, but price is not the only indicator of oil quality, depends a lot on sales focus of outlet.