With the choice of the Zillertal you normally can´t do anything wrong. There are many beautiful skiing areas even a glacier is over there where you can run ski all the year. You can buy for the whole Zillertal one card so you have the choice to change whenever you want but normally not necessary because all the areas are so interesting that you won´t get bored.
Kaltenbach has a huge amount of slopes and lifts. You will find the slopes in all different difficulties and additional you have a big backcountry area beside the slopes. All the slopes are very bride and the runs are very long so you are most of the time and the slopes and not on the lift. Unfortunately in the main season there are many people so it is bether to go there in January or after February. But because of the many people you will have a better time after skiing on the après ski.