Personally, I prefer Louise. The runs are longer and steeper and the whole back bowl area keeps sweet snow for the whole year pretty much. Yes, sunshine gets more snow but I think the back bowls can match it with snowfall and whats blown in there combined.
Only The Dive and Wild West at the shine can match Louise for quality terrain but to go in them you need to have avy gear, plus they're closed a lot and the laps can take super long.
Parks aren't even a contest, Louise kills it.
All these things said, I've had some great days at sunshine but my ideal situation would be living in Banff and working at Louise.