You will get all kinds of answers on this one !
Here is what I use.
Klotz RC Model Lube I use it in 5cc engines and up.
I mix it with LL100 aviation gas for use in small gasser engines. Why? Because of the lack of smell compared to regular auto-grade pump gas. The planes can be brought inside the shop after running and not stink it up with the eye burning stench you get from pump gas.
The Klotz smells good too and it doesn't leave much residue at 20:1 ,32:1 and 40:1 mixes.