Having never been to either and wanting to go to both... Whistler wins for the skiing terrain. I have always loved the dramatic pictures of the Banf Springs Hotel and would like to include a few days there in extended powder highway loop at some time in the future.
BTW, didn't a woman get killed by a mountain lion while XC skiing out there a few years ago?
I am trying to get my ski club to do a Whistler trip to make it more affordable.
Going early or late season makes it reasonably affordable. Late season (mid march and on, also typically has fantastic conditions, and more sun (which is often missing at WB), and good rooms can be had under $200 / night (often much under). They often have "rest of season" passes too, which are pretty cheap. Fly into Sea and drive up will typically cut hundreds off the airfare.
For the price of least coast you could be at WB