Here are my opinions on a few stages:
Castle Siege- i love the idea of the stage changing its entire layout often. It will make it feel exilerating everytime that i play on it.
Battlefield- Awesome idea of changing the time of day, i will enjoy brawling during different periods of the day.
Delfino Isle-The different sections of the whole stage will really test you to fully use your enviroments to their full potential. You'll need to adapt to different flows of battle as you play.
Norfair- Interesting now that lava flows from different places. And that safety pod thing will make you quite competitive. I like competition.