You'll want to ski at both for sure. You'd be bored if you spent an entire week at only one place.
My opinion is that Sunshine has some nice natural freeride terrain and better snow, but Louise has more variety and longer, steeper runs. The park at Louise is huge - most of it terrifies me.
Snow conditions are adequate at the moment, but not amazing (it hasn't snowed much since December). Last year, March was insane so if you are flexible maybe come out in March rather than February.
If you want any other suggestions, let me know...