Commissions traditionally are 5-6% in the city. However, all the development in Chelsea and the Financial District that has been happening the last couple of years has changed things a bit. Sponsors are commonly offering 4% to the buyer's agent. If you are paying a 5%commission, bear in mind that the buyer's agent and seller's agent split that (actually their companies split it and then split it with the agent). Similarly a 6% commission is split 3% and 3%. A full 90% of real estate deals in NYC are agent to agent or "co-broked." So when you list it with your listing agent/sellers agent, bear in mind that your buyer will probably be brought by a buyer's agent rather than an individual finding you on their own. Buyer's agents are more likely to go where they can get 3% or 4% than 2.5%. So saving on a commission might actually cost you more because you will get less traffic and thererfore less attractive offers.
That said, your listing agent should be with a company that will give the broadest possible exposure to your listing. As my colleague mentioned below, Coldwell Banker Preview International is the only local, national and international company in NYC. Furthermore, we are REALTORS, which most other NYC companies are not. This means we belong to the National Association of Realtors and have to subscribe to the highest code of ethics, much more stringent than that of the Real Estate Board of New York (REBNY). It also means your listing will be on Realtor.com, as my colleague mentioned (and 65 other sites). Realtor.com is the most heavily trafficked real estate website, and and the second most trafficked website second only to E-Bay. Additonally, your agent should be someone you click with and feel good about. Preferably they have been recognized by their company in some way. If you would like help from someone who fits all of this...feel free to click my contact info and get in touch.