I despise Kennedy Airport because it's crowded beyond belief. Now, Stewart only had two flights operating when I was there. TWO — one flight to Myrtle Beach, South Carolina, and one flight to Iceland — and I was through security in three minutes. The airport was so clean that I could have eaten off the floor (not that I would), and it actually felt peaceful to wait for my flight. I'm so used to the hordes of people at central New York City airports that this small detail felt divine.
Con: The drive is about an hour and a half if you're located in NYC. Granted, the route was beautifully scenic, and it cost about $75 to park my car for six days. Split between two of us, that price felt fair. That's less than the price of one Uber from my home to JFK. And if you don't drive? There's a Megabus that takes you directly from Port Authority to the airport.
The location of this airport is actually fantastic depending on where you live, though. For my friend based in Westchester County, for example, the distance to JFK and Stewart is roughly the same. The same goes if you're based farther out in New Jersey!
Would flying out of Stewart be my first choice? Because of where I live, no. But I wouldn't dismiss it entirely, given how small and well organized it is. If it weren't for the driving distance, I'd pick Stewart over JFK always.