Amsoil is marketed and sold via a multi-layer pyramid scheme, so not a very good value in motor oils. The oil is (probably) fine but it is marketed too aggressively with all kinds of unsubstantiated claims of its superiority. That alone puts me off it, regardless of the price. It is the Dyna Beads of motor oils.
I can only go on my own experiences and the experiences of my friends.
A friend, for instance, recently sold a '99 Tundra that'd had gotten oil changes at 16,000 to 20,000 mile intervals using Amsoil. It had 270,000 miles on the clock when he sold it and still used no oil and ran like a top. Would it have done as well with some other oil? I don't know. My commuter car was a '97 Cavalier that I bought with 132,000 miles on it. I sold it at 241,000 miles, and it was using a pint of oil every 4000 or so miles at that point. Everything else was breaking, but the little engine was still running fine. I changed the oil once a year with Amsoil -- usually around 16,000 miles. Again, I don't know how it would have fared with some other oil. My Goldwing went 11 years and 111,000 miles with 12 oil changes. It used no oil when I sold it.
It's worked for me
I have considered going to a lower priced oil now that my annual ,mileage is down, but it wouldn't save me much, so I guess I'll keep pouring that $10 / quart oil in my stuff