Final answer:
Almond milk is the best substitute for coconut in a Piña Colada as it offers a creamy texture and can blend well with the other flavors of the drink.
Step-by-step explanation:
When looking for a substitute ingredient for coconut in a Piña Colada, almond milk would serve as an effective non-coconut-based alternative due to its creamy texture and nutty flavor which can complement the other flavors in the drink. Although options like banana or mango puree can add a different flavor profile and thickness to the cocktail, they do not offer the creaminess that the coconut brings to a Piña Colada. Meanwhile, pineapple juice is already a key component of a traditional Piña Colada, so increasing its quantity won't effectively replace coconut's role in the beverage.