Is Valvoline a good motor oil / transmission fluid company?
Yes, Valvoline makes good oils and ATF fluids.
I personally have been using Valvoline products in every vehicle I've owned for the past 45 years, and I know that my dad always used Valvoline products too. I think their products are excellent!
But with that being said, there are many brands of lubricants and other products that have loyal customers and Amsoil is one of them so I don't see any need for you to switch.
It's all about specifications with oil. You manual should state the minimum standard that the oil should meet (eg API, ILSAC etc.) This describes how the oil behaves under test conditions. When you go to the store to buy your oil, you look at the bottle and it will list the standards that it meets. If it meets the standards that your manufacturer has specified, then you know that engineers have deemed it suitable to put in your engine.
Ignore the brand names. They all get their base oil from the same places.
@mountainmanjoe
Very well stated. It's not about the brand name, it's about the rating and what standards it meets for your specific vehicle.