Norse Atlantic from Gatwick to NYC and Gatwick as opposed to Heathrow airport

I can't help with the airline apart from to say you need to check if there are any add-ons that you might want to pay for such as checked bags and seat reservations.

As for the airport there is precious little to choose between Heathrow and Gatwick. Both are very busy airports used to handing many flights. Access to Gatwick is good and especially so if you stay near one of the two main train lines to there from central London. Don't whatever you do consider any form of road transport to Gatwick though.

Both are easy to get to from central London by train - Gatwick takes a bit longer.
I find Gatwick smaller and more user friendly - it can still be busy, though.

Well, I loathe Gatwick (too far from my area of London, too small, chaotic) but for that price difference I’d deal with it. Just make sure that you are including all the possible extra costs in both journeys

I have flown on Norse. Be aware that everything is extra--meals, blanket, and of course, luggage. I did it because I had a nonconnecting flight to Sardinia that was flying out of Gatwick and did not want to contend with switching airports. It actually was not that much cheaper once I added everything on but that was not my prime motivation.

Pros:
cheaper
bought food for trip back and best airplane food I have ever had

Cons:
Could not check in online and very inefficient at checking people in. I would pay extra for express or whatever it is called. I have never stood in line so long to checkin.
My seats over the sea did not recline. Think Spirit airlines. Coming back they did.

If you go to Gatwick, don’t use the Gatwick Express. You can get a train operated by Southern Trains from the same London Station (Victoria) that takes 3 minutes longer and is much cheaper. You can also get to Gatwick using Thameslink trains from Farringdon or London Bridge.

The train station is linked by a bridge to the south terminal and there is a small, free shuttle train to the north terminal which takes a few minutes.

No personal experience, but found this review an interesting read--
https://davidwilliamrosales.com/2024/11/27/norse-airways-review/

This one also had some interesting observations as well--
https://www.frommers.com/slideshows/848581-what-is-it-like-to-fly-norse-atlantic-airways-our-review/

When comparing the cost be sure you are doing an "apples to apples" comparison

Norse is the newest trans-Atlantic low cost carrier. I have not flown them but they do the type of pricing where you have to pay extra for everything (altho to be honest even the legacy carriers do this now). In terms of airports, to me the only big difference between Heathrow and Gatwick to concern yourself with is how easy it is to get there from where you are staying. As mentioned above Gatwick is easily reached from Victoria (via Southern Rail or the more expensive Gatwick Express) or if you're coming from further north or east you can get the Thameslink trains that go via London Bridge.

We took Norse Dulles into Gatwick. We chose the upgraded economy and found the service to be much better than expected. The upgrades brought the price more in line with competitors; but we would definitely choose this solution again.

I prefer Gatwick as I can catch the train to a station five minutes from my house. It's a smaller airport than Heathrow but still very busy however I've found that security is marginally more efficient and immigration has always been very quick in my experience, often with no lines at all.

I've never flown Norse but I know that they only fly Dreamliners so that's a positive as a number of airlines are starting to fly Airbus A321 neo aircraft on long haul routes which are narrow body, single aisle aircraft and are not suitable, in my opinion, for long haul flights.

Thanks to all for your responses