Flying to London is convenient no matter where you are flying from. There are direct flights to one of London airports from almost every city in the world. There is also always a flight with connection, sometimes it is even less expensive to take a flight with connection.
Flights to London arrive to three major London airports:
Transportation from all London airports is convenient, so if you have doubts what airport of arrival to choose, base your decision on connection times and airline ticket price.
Most airlines fly to London. British Airways is UK's major carrier, but flights are also fulfilled by other airlines: United, Delta, Virgin Atlantic, KLM, Air France, Lufthansa etc.
Flights are usually less expensive in January and February, higher during holiday times and school vacations, and in summer.
If your schedule and budget allows, it might be a good idea to take a flight with connection in one of European cities and diversify your travel experience. Most European airlines have direct and convenient flights to London.