I only observed these in 2015.
For flavor and heavy production and more lateral growth habit and lowish-to-medium vigor, the M-4. But the original tree is said to be an every-other-year producer--- that is why it hasn't been promoted.
I also very much like the flavor of the Cotton Candy, and its sturdy, upright growth habit and non-exagerated lowish to medium vigor. It is said to be a more dependable, annual producer.
If I had a tiny property to plant mangos, I would buy either one of them, and then, 3-4 years later, I would top-work graft a few of the branches with the other variety.