Having been to both cities many, many times, and assuming you have not visited either(????) It depends on how long you are going or planning to stay, how flexible you are with regard to staying in a 'proper hotel', or if you are cool with keeping it simple to save some money for other things, and most importantly in my opinion, if you need to see the touristy things in each city. For example, if you have solid plans to see things like The Statue Of Liberty, Empire State Building, etc in NYC, or in LV, things like Penn & Teller, Hoover Dam, etc. Seeing these sites are expensive, and add up quickly. But for most people, they have to be seen. A bit like going to Paris and NOT seeing The Eiffel Tower. If you do not particularly care for spending copious amounts of money and time seeing these things, I believe you will have a far better time in Las Vegas. There is so much more to do now than just gamble, the restaurants rival any big metropolitan city, and LV is compact. You will spend a small fortune in NYC just getting from A to B. Trust me. Also, Vegas is far more accommodating and certainly more friendly than New York without a doubt. Ask anyone who has been to NYC multiple times, or anyone who lives there for that matter and you will hear the same phrase: 'New York is the center of the universe. We have everything here, and everywhere else sucks'. NYC obviously has cool things to do and see, but for me, my money, and overall reflection of the trip after I get home.....Its Las Vegas.
Hope it helps. safe travels either way.
Peace be with you.