Firstly, what would be the reason you need this? :) Secondly, here's my answer.
Storms ability of being able to controll the whether. It is a very powerful power when you think of all the possiblities used with it.
Thirdly, if this is for any characters in a book, I would say please let us people know so we can know exactly what your going for. I know the title says what's your x-men power, but if you are using people's results for a choice on what character should have the most popular power. Thanks for your time.