I found it could be great to have a button (apart from the target method options) that allows me to indicate a tower it should prioritize targets to which can make 150% damage over other targets.
As an example if you select that option:

• the sniper will prioritize targets of the type "Strong" over "Fast" or "Regular" , but if no "Strong" is present, it will aim according to the target method selected (First, Last, Weakest...)
• the cannon will prioritize "Fast" or "Icy" over "Strong" or "Regular" or any other type of enemies. But if no "Fast" or "Icy" are at range, it will target according the selected method.
  I suggest this button can be used (or not) for each type of tower which is more effective against certain type of enemies (all except the Freezing tower".

In any case, I just started playing this game and so far, I love it.

Cheers!