Anytime is the best time to visit New York. However, to enjoy New York to its fullest, it is best that you match your mood according to New York's seasonal personality. For instance, winter (December to February) is the month when New York's cultural side reaches its peak. It is the time when Broadway, Lincoln Center, the Metropolitan Opera House, along with several other 'high art' cultural venues, get throngs of spectators. Be aware, though, that winter is one of the priciest seasons to catch a performance of art. Winter is also optimal for heading upstate, near the Adirondack or Catskill Mountains (near Canada), in order to get physical with some snow sports like skiing, sledding, or snowboarding.
Summer time (June to August) brings free art to the masses with the popular 'Shakespeare in the Park' held at Central Park. It is the season when New York's most talented classical actors rehearse and perform one of William Shakespeare's plays for free in order to culturally enrich the city. Summer is also a favorite time of year for the gourmand and epicureans alike, especially since top dining venues offer incredible discounts along with there being many free wine-tasting events. Yet, summers in New York can get uncomfortably humid, and for this reason you will find that most New York City residents drive out for the weekend to places like the Hamptons, Cape Cod, Fire Island, or the Jersey Shore.
Spring (March to May) and fall (September to November) offer the best weather. Spring is the least tourist trodden season, though this isn't saying much since New York is a heavily populated city. Yet, if you want to enjoy a piece of the apple with the least interruptions, then is the time for you. Spring also offers some great sales, so this season is perfect for the penny-pincher in you.
Fall, on the other hand, tends to be quite festive with Halloween and Thanksgiving being two major holidays. Fall is also one of the most picturesque seasons with its orange, red, and brown hues.