Amsoil makes good oil if you use their full synthetic oil because they use a group IV PAO base stock instead of group III conventional base stock.
groups I, II, and III are all conventional oil with group three being the most refined meaning they remove the most impurities from it over group I and II.
The oils molecules are still conventional oil meaning they are different sizes and shapes example.
The smaller molecules in conventional oil get used up faster than large molecules.
In a true synthetic oil the molecules are made in a lab so every molecule is the same example.
Now seeing the difference in the molecules lets you understand better why a synthetic oil can protect better and lubricate better then a conventional oil, i.e. you don't feel the shifter get harder to shift as the oil gets miles on it.
With a synthetic oil having every molecule the same size they share the work load on a bearing surface or gear surface better than a conventional oil does. With the conventional oil the larger molecules are doing more of the work load but the smaller molecules are being used up so over time you have fewer molecules to do the job in a conventional oil vs a true synthetic oil.
What is a true synthetic oil, they are the group IV PAO oils with all other synthetics that are not in group IV PAO group placed into the group V category which will include ester based oils like Redline oil.
Both group IV and group V are man made with every molecule being the same as the others.
Group V synthetics have one advantage over pure group IV synthetics and that is a group V ester based synthetic carries a positive charge like a magnet so it clings to metal surfaces. That is why a lot of group IV PAO synthetics will add some group V ester to their formula. Group V oils will add some group IV PAO to their formulas because a pure ester group V can cause seal shrinkage resulting in oil leaks, by adding some group IV PAO which can cause seal swelling takes care of that issue so you won't get an oil leak.
I personally for me like Redline group V oils for my cars and motorcycles.
Here is a little known fact about semi-synthetic oils, by law a semi synthetic oil can not contain more than 30% synthetic oil in it. That means that 70% of a semi synthetic oil will be conventional oil, but it could also mean 99% could be conventional oil as there is no set standard for how much synthetic has to be in the semi-synthetic oil other than it can't be more than 30% synthetic.
Now group three conventional oils are also called hydro cracked and due to a ruling made by the NAD (National Advertising Division) said that Castrol could call their group III oils full synthetic when Mobil challenged Castrol.
No matter what NAD ruled group III oils are still truly nothing but a more refined conventional oil with different size molecules. Sadly the API followed the NAD ruling and call group III oils full synthetics.
Interesting note on this is that in Germany only a true group IV or group V oil can be labeled as a full synthetic, group III oils can not be labeled as synthetic oils well because they are not synthetic oils. NAD and the API have done a huge disservice to the American public by allowing oil companies to falsely label group III oils as full synthetics.
If you want a true full synthetic oil purchase only oils made from group IV and or group V base stocks.