From my experience the most mathematics entrance (Basisprüfung) exams at ETH for CS are harder than the equivalent at MIT. At MIT it is harder to get in whereas ETH the first year is harder and there are a lot of drop-outs.
Just make sure you are confident on your theoretical skills before deciding.
I would just like to add a component to this lively discussion.
If dreaming about living in Switzerland, learning German and attending ETH is providing you with inspiration, then do what you can to make it happen! Yes, MIT or Wisconsin or another American school may be more practical, but practical isn't always going to inspire a person to do great things.
I think it is great that you are getting all of this valuable advice.
But if life is Switzerland is motivating you, go for the dream.