Congrats !! Two acceptances and two waitlist situations (which are more likely to turn into acceptances than not) must feel really good. In my opinion, I would wait as long as possible to make your decision. The two schools that have offered you admission can't take it away from you before April 15. And who knows, maybe if you get off those waitlists before April 15, those new offers might be more enticing. Also ask yourself which school is best for you.
You have time to think on it which is a great place to be.