I recently changed out the transmission fluid in my MTX-75 for Ford XT-M5-QS fluid. The dealership didn't even know what this stuff was and had to order it. This is a hillbilly town though. If it isn't a truck or V8 they don't know anything.
The transmission with it's new fluid and Poly lower mount, shifts 100% better.
You could use anything in the transmission. Cooking oil if you wanted to. But what is the "best" for you, isn't always the "best" for someone else.
My daily beater doesn't take the beating like a drag or Auto X car does.