Is Gatwick or Heathrow more convenient?

Depends on where in London you are going.

Gatwick is much smaller and easier to deal with. But, as mentioned above it might depend on where you need to go in London.

One advantage of Gatwick, if you are also flying out from there, is that your round-trip train tickets to and from London will give you access. The Days Out 2-4-1 offers on many London attractions.

https://www.daysoutguide.co.uk/2for1-london

You need paper tickets bearing the National Rail logo; mobile tix on a phone are not valid.

more convenient to what? The Natural History Museum and the V&A and the Royal Albert Hall or the Eurostar train or the Bank of England? or what?

All depends on where you are coming from and going to.

I like Heathrow even considering its size as the flights I need to take are both more convenient and plentiful, so if I miss one there are several others to choose.

Since you're flying to/from JFK, you probably have many choices as far as airlines and nonstops, into either LHR or GAT. So I'd go with price and convenience. Also know that a few airlines have a day flight to London (generally LHR) if that's something you'd prefer instead of an overnight flight.

I like Heathrow because it’s on a tube line. But I’m a solo traveler and I have no problem riding the tube with my luggage. The last two times I’ve take the day flight and have stayed at Premier Inn Terminal 4 and then gone into the city the next morning.

Gatwick is my default airport and has improved over the past 2 years now the refurbishment is complete. I always get more delayed at Heathrow.

Whereas I personally dislike Gatwick a lot, but find myself having to use it more than I would want to as many more leisure-orientated destinations are no longer available from Heathrow.

Gatwick offers the ability to skip the passport line for a fee. Although that may not be necessary for American travelers anymore thanks to EGate.

Gatwick is less busy and an easy train (not tube) into Victoria. I have found the train situation a little more confusing navigating out of Gatwick than Heathrow. I do like the view you get in the daytime heading from Gatwick into London. You pass through London Bridge and see the Tower and Gerken up close.

The best part about Heathrow to me is the Heathrow Express train into London. 15 minutes.

So it’s really a question of where in London you are headed and the cost of the flights. In either scenario, be prepared to use public transit to get into London.

so, maryellen, where do you want to get to? Are these comments helpful?

@ Kevin...this is true of all UK airports and rail stations now, not just Gatwick....wherever e-gates are available. Something like 15 different locations.
Personally, I choose the airport based on the airfare. If there is little difference in price, then I choose based on where I am staying in town. I always take the Express train for either airport so if my accommodation is convenient to the the Paddington side of town I'll go into Heathrow. If Victoria Station is more convenient for me then I'll fly into Gatwick.
If I'm taking the tube to my location from the station, I also think about how many changes I need to make and choose the station/airport with the fewest changes to make it easier with luggage. I usually take a taxi from the station though so not a huge consideration.
Really though, one is no easier than the other IMHO. Both have the Express. Both have excellent public transport links. Both have private car / taxi / Uber availability. Gatwick is a bit further out than Heathrow but the time difference to get into town is no more than about 15 minutes no matter which kind of transport you choose.

I'd say Gatwick and Heathrow are as good as each other, however a few points to consider, Heathrow is on the Piccadilly tube, so very convenient for accommodation around or near that line, Earls Court/Gloucester rd, the Heathrow Express gets you into Paddington station, and in the not too distant future the new Elizabeth line/Crossrail will have a service from Heathrow, west/east across London.

Heathrow also has TFL rail to Paddington, this was previously known as Heathrow Connect.

Be careful about early flight check-ins the Piccadilly line only runs 24 hours on Friday and Saturday nights.

Gatwick has frequent train services to Victoria station and on the Thameslink service to Blackfriars/Farringdon/St Pancras, there are late/early trains, weekends can sometimes mean track work, so journey times can be longer, or partly by bus.
Gatwick is now within the Oystercard boundary.

London City airport in Docklands, is small, convenient, with a DLR station, has good feedback, I don't know all their destinations though.

Stansted/Southend/Luton are more distant and not as convenient for journeys to Central London, especially with early or late transport journeys.