Any 2 stroke oil bought today will be 100% better than any oil available when the mower was made.
All 2-stroke oils now days are ashless & low sulphur , mix better , stay in disperson in the fuel tank and drop out under compression pressures .
SO don't fret.
Modern marine 2-strokes are usually vegetable based oils to reduce pollution of waterways
So buy what ever the local store sells and go for a mid priced oil or if it makes you feel good the highest priced oil.
Obviously the cheapest oil will be the worst as it is blended down to the lowest price using the lowest priced ingredients.
FWIW I am using Stens 2 stroke at the moment because when All power went bust they were selling it below cost .
I like to use the chamber pack and only sell chamber packs or 4 liter refils for pollution / landfill reduction reasons .