Cheaper to fly out of New York for Christmas Holidays?

Hey everyone!

So I want to get away for the holidays and thinking of somewhere hot, so basically the Caribbean like Dominican Republic (but not Cuba since we already went there this year) and we wanted to leave around Dec 17 (late at night) or Dec 18 (anytime) but it really depends on the route we will take.

I have a travel points card that will give me 2 roundtrip flights free to NYC. Seeing how we want to stay in NYC for New Years I figured we can fly there early and get a vacation package out of NYC and come back for new years.

Problem is, vacation packages seem to be more expensive out of NYC and the free flight to NYC goes to Newark or LaGuardia not JFK which I think would be the best airport to fly out of if I'm going to the Caribbean.

Anyone has any advice on this? Would it probably be best to just fly out of Toronto? And just fly over to NYC after my trip? Anyone know of some great US vacation websites?