Both are very different. I would think about:
1. ages going on the trip
2. time of year the trip is being taken (NY is cold in winter, Disney is hot in summer)
3. what you're looking to get out of the trip (NYC can be very educational in addition to the shopping vs. disney is more rides and magic fun for all......depends on what you are interested in though, as MOMA might be amazing to one person but a total bore to someone not into art, etc.)
4.what you're wanting to spend on it (disney can be all inclusive with a meal plan,transport to/from airport,hotel and park tickets all together in a vacation plan you make online/over the phone. NYC is more everything costing and planned individually so it really depends on what you want to do there for how much money you spend)
One vs. the other is really just up to a person's preference and circumstances.... think about what best fits you and either way i'm sure it will be fun! :)