December is a good time to visit the city has a great Christmas feel to it. Rockefeller Centre has the big tree (and small skating rink, larger one in central park), 5th Avenue will be set up for the celebration / retail frenzy
Weather could be all over the place, clear and sunny, freezing cold or just wet.
Hotel prices vary quite a lot and can be pricey to mind boggling, that may define your budget/trip.
What sort of thing does the Mrs like, shopping, sights, food, bar scene, arts ? What sort of hotel, traditional, hip, budget or apartment style ? How long a trip are you planning ? The great news about New York is you can do any and all of the above.