I've seen Lake Louise, and it is beautiful. As is a lot of the scenery around Banff. I've also seen the Alps and I'm hoping to get a look at Mt. Everest next month (while flying between Calcutta and Delhi). Of course, living in Colorado I've seen plenty of beautiful mountain scenery. I tend to think whatever especially awesome scene I'm currently looking at is the most beautiful ever, so I'm not a good judge of whether Lake Louise is prettier than the Alps.
My personal favorite is anywhere where I can have a 360 degree view of mountains after mountains after mountains stretching away to the horizon. There's one 4 wheel drive pass we go on a lot near here where you get that kind of view from the top. The only trouble is, you can only get to the top from about the middle of August through the middle of September. That's the only time the road is clear enough of snow. Ok, I think that's enough rambling on for now! It's way past my bedtime.