The holiday party season is followed by the season of remorse. Now we eat, drink, and make merry. After January 1, we diet and work out. Each year, gym attendance soars after New Year’s Day. But which gym is right for you? At first, New York’s offerings seem limitless and the choices difficult. But the market is actually pretty well segmented to let you choose how much you want to pay for what level of service. Plus, at this time of year, several gyms are offering inducements to sign up.