Gatwick is a bit more awkward to get into town from, but that does depend on where you are staying. If the price is significantly better to LGW then I would be very happy to choose that over LHR. But make sure you are comparing eggs with eggs, as a number of flights from North America to LGW are lost cost operators that may have plenty of extra costs. I also hope you are looking at airline websites to price up rather than one of the shonky online agents.
I would base it on routing/schedule/price
Since you are starting from NYC, you have lots of flights into LHR. I don't know if I would go out of my way to avoid it and pick LGW. unless maybe the price difference was large.
If you were starting in a city that had direct non-stop to LGW and mot LHR, then I may not go out of my way to get to LHR.
it's like starting from JFK or EWR - in the scheme of things it hardly matters
Agree with JeffM; on our flight this week we have to pay for luggage and meals into LGW; the carrier we used last year, those were provided.
I find getting from Gatwick to central London is quicker and easier than Heathrow. The trains ride can be as quick as 30 minutes and services leave every few minutes. If you're heading to Wimbledon or near, that's easy from Gatwick, simple change at Clapham junction.
Costs slightly more, to any central London rail terminal: Gatwick is £8.10 versus £3.10 from Heathrow (quoted fare is off peak using oyster or contactless).
Does depend on where you plan to stay, but I agree in the grand scheme of things makes no difference.
Heathrow is better connected to more places in the city, but if you're saving good money on the flights...
if i had a choice i would choose Gatwick.
i feel its smaller and less walking from Terminal to train.
They're both fine for central London. Depending on where in London you're staying one airport may be slightly more convenient than the other but it's close. Both have solid frequent and affordable rail connections (and not just HEX and GEX).
If you're looking at flying Norwegian make sure to work out the total cost, not just airfare. Norwegian lowballs on airfare but then you have to pay for checked bags and meals and drinks. On the comparisons I've tried for the Air Travel forum once those are factored in they're only slightly cheaper and in some cases more expensive than Delta, Virgin, BA, AA and United. And BA flies JFK-Gatwick so you may find that cheaper than the mainline carriers to Heathrow, and comparable if not overall cheaper than Norwegian.
I live in the City, which is just inside the eastern edge of the Circle Line.
Gatwick by Thameslink is easier for me than Heathrow and I prefer it.
IME The Thameslink trains are more comfortable than the tube and Gatwick is easier to navigate than Heathrow.
If you are staying around Victoria, the Southern trains from Gatwick are marginally easier than the tube, changing at Hammersmith.