Thameslink or Gatwick Express

Where in London are you staying?

12:50 pm (just after noon) or 12:50 am (just after midnight)?

The difference is where they go and how fast they get there, and that one is a commuter train and cheaper and one isn't.

You left out Southern.

All three are operated - at the moment - by one company.

We will be staying in Myddleton Square which I think is closer to Kings Cross. Is there any upside to one or another?

Thanks.

Just after noon. Sorry....

As you are near Kings Cross, use Thameslink directly from there. Not only will it be cheaper it will be more convenient and probably quicker.

Thank you for theadvice. Is there a benefit in buying tickets for mid-April online now?

All the fare details are on the Thameslink page.

https://www.thameslinkrailway.com/destinations-and-offers/airport-travel/gatwick-airport

An anytime single from St Pancras International (they go from St Pancras, not Kings Cross across the street) to Gatwick is £12.10. Walk up and buy your ticket. If you want to buy ahead and can sand a Super Off Peak you can spend as little £9.70 but for just about £2.50 savings is it worth it?

A frequent service, at least 3 times an hour, you can also board at Farringdon, City Thameslink or Blackfriars if you find any of those more convenient on the day. Takes between 45 minutes and an hour, no changes.

You can also use your Oyster Card or other Contactless method such as Apple Pay but I haven't checked the price on those.

The trains have no doors between carriages, large screens informing you of the progress of your journey, and not terrific seats but what do you want for less than an hour...

When using the Oyster Card to pay for the Thameslink from St Pancras to Gatwick, it is less than the normal ticket. In 2017 it was 10 GBP something, takes one hour. I did it twice in 2017.