Los Tuneles was the best tour I did in the Galapagos, especially for snorkelling but walking on the volcanic structures and seeing blue boobies there was also special. Swimming with turtles, pools of sleeping sharks in caves, sea horses, and fish. Decent visibility (best I had on the islands). Darwin was a great guide as well. Highly recommended.
For what it's worth I also did the Tintoreras tour and , tbh, compared to Los Tuneles it wasn't really worth it. Poor vis and not much to see.