Talking about oil is akin to talking about religion. There's many opinions. Here's mine.
My knowledge of today's oils is that the difference between conventional and synthetic is merging. Conventional oil is made from group 2 or 2+ base stock and synthetic is made from group 3 and/or 4 base stock (keeping it simple). The additives are every bit as important to the final product. Its my understanding that in order to make today's thinner oils such as our 5w20, even a conventional oil has a bit of synthetic in it (thus, the merging comment).
My belief is that synthetic oil is only marginally better for a few aspects. It might flow a tiny bit better at very cold temperatures. It might handle extreme heat a tiny bit better (turbo applications). Its best attribute is that it should last for a longer oil change interval. What I believe that it does NOT do is appreciably reduce engine wear under normal conditions. Tons of used oil analysis at Bobistheoilguy forum show this.
These are generalizations. In Minnesota with sub zero f temps., a synthetic might help. If you are doing 3K to 5K oil changes, you probably will not see less wear using a conventional vs. a synthetic. If you want to go beyond 5K oil changes, then the synthetic is "probably" a better choice. Some people ARE doing the long intervals with conventional oil with success. It depends on the conditions, hard vs easy miles, and the vehicle. Our engines are generally easy on oil compared to the newer direct injection or turbo engines.
Some claim that changing to a synthetic after years of conventional will "over-clean" the seals and cause leaks. This is based on experiences MANY decades ago. But, it is still a very controversial and contested subject. Many (most) believe this is no longer a problem.
I use Pennzoil Platinum synthetic and change my oil about every 7 K miles. In the past I always used conventional oil at approximately 4K intervals. Used oil analysis is the only true way to know. Plenty of people are getting 200K+ miles out of their engines using either conventional or synthetic, so toss out the idea that a synthetic will magically make your engine last longer.