What everyone is saying about Sunshine having flat spots and shorter runs is true, Louise is the better hill as far as the vertical goes. Louise would be the perfect hill IF it had the snow that Sunshine gets, but it's not even close. Getting great snow at Louise is a rare thing. I hate riding on ice and dodging bare patches, so I prefer Sunshine. The one big plus for Sunshine is the consistent quality of snow. They don't make snow at Sunshine, it's all natural and it will be you best shot at powder when you're here. If the gods are smiling down on you, you might get some powder at Louise, but you usually have to hike for it.
I've had some epic days at Louise, but they always felt like a once in a lifetime thing. I've never had a bad day at Sunshine, but that's cause I value the snow quality over everything else these days.