I believe NYU med has one of the most coveted derm programs in the nation. You go to NYU, and in-house, you are probably a shoo-in (I am assuming you'd keep up the good work in med school that got you to all these great schools in the first place).
If not NYU, then Harvard.
And honestly if you want to do straight cosmetic botox etc derm then it makes sense to be in NYC, that's where all the high rollers would be
Anyway you cant go wrong with any of these schools. best of luck.
EDIT--> Actually looking at the match list on the derm board, none of the NYU spots went to NYU kids. 2 of the 7 went to Harvard grads. 3 of the 5 Harvard derm spots went to Harvard. 2 placed at Northwestern, 2 at UCSF, etc
nEVER MIND what I said earlier. I think its clear. Go to Harvard. Like 10-15 kids apply for derm each year, which may make it competitive within the class, but it doesn't look like places are ever gonna turn down a Harvard grad (i know, i know some do but you know what I mean).
And dont worry about the $$, I mean... you do want to be a dermatologist, so I'm sure you're gonna pull some serious bank
(I'm being facetious and serious all at once)
good luck!