I honestly think in a 1v1 combat situation, the Rasenshuriken would be stronger but only for one reason;
The Rasenshuriken attacks the body at a scale that it actually attacks the cells in someone's body, making it extremely deadly if it connects with anyone. The mini bijuu dama is just a massive blast of force that would KO someone if it hit them directly, but it's easier to avoid then the Rasenshuriken and isn't as deadly on a scale that it HAS to be a direct hit for a kill.