Once at the airport, whatever that airport is, you always have several options available to you in order to reach Central London.
From Heathrow, you can both ride the tube, a coach or a, definitely more expensive, taxi.
From Stansted Airport you can either ride a train, i.e. the Stansted Express, but note that it will terminate at Liverpool St. Station, a taxi or a coach.
Should you opt to use a coach, you can both reach Central London by the National Express Services (Single ticket £10, return ticket £17) or a Terravision service (Single £9, return ticket 14£). As you can see there is a small difference in price between the two companies, but you’d better decide which service use according to your final destination in Central London.
Should you need to get to Golders Green, St. John’s Wood, Marble Arch and Baker Street, you should use the National Express services. If you need to go to Victoria Station or Liverpool Street you can both ride a National Express or a Terravision service. You can also buy a coach ticket with Easyjet when you book and buy the flight online.
London City Airport is actually located in Zone 3 of London and you can comfortably and conveniently ride the DLR (Dockland Light Railway) to reach Central London.
If, instead, you arrive to Luton Airport, you can reach Central London both by train and coach, a taxi still remain a more expensive, but available, option.The trip by train, although not particularly nightmarish, is a little bit more complicated, you need in fact, to catch a bus at the airport which will bring you to the Luton Parkway railway station, than ride the train to Farringdon, where you be able to finally take the subway.
Also from Gatwick Airport Central London can be reached by different means. By train you can ride both the Gatwick Express and a Southern Train, usually calling just a couple of times before arriving to London Victoria, where the train terminates.
If you should decide to travel by a Southern train, be aware that you can book your journey online and save some money. Advanced online booking, in fact, can also allow you to just pay as little as £3 for each single ticket (usually costing at least £9 during off-peak periods), the only problem being that you need to book for a specific train. If this could be easy to plan for your coming back journey to the airport, it is not exactly so when you arrive. In fact, it is rather tricky to exactly predict beforehand if your plane will land on time, how long it will take to claim you luggage and to pass the passport inspection.
If you want, instead, ride a coach be aware that at Gatwick, differently from Stansted and Luton, coach services are operating during a limited period of the day, or put it in another way, they are not operating round the clock.
Taxi, also in this case, obviously is amongst the possible viable options.
