There are a number of things in our hobby that have two correct answers. Fuel is one of them.

100% synthetic fuel works great for most flyers. Especially the ones who know how to set a needle and do so when needed. It might let down a few flyers who are careless.

Castor/synthetic fuel works great for most flyers who use it. There is somewhat of a safety margin in it. It might let down a few flyers who are sloppy.

Two fuels, two correct answers. But neither works 100% for 100% of the modelers.