I've been to Shake Shack in NYC as well as on the strip at NYNY. I've always been a fan, though I won't say that it's better than In N Out. Apples and Oranges.
I went to this location shortly after they opened, and although the food was great the experience was a bit hectic due to all new staff (I suppose). Also, you will find a bit better beer selection at NYNY vs DT Summerlin.