If you ask frequent travellers going to or departing from London what is their biggest advice, they will often answer: avoid Heathrow. The UK main hub, one of the busiest airport in the world, has had a long reputation for its problems, delays, congestion, baggage lost and unfriendly for most passengers. However a big hope was lifted a few month ago by the opening of the new Terminal 5 on March, 27, dedicated to British Airways sole occupier of the new building. The result was a shameful fiasco with tens of thousands of baggage lost and the nightmare for travellers lasting days as BA and the airport owner BAA were trying to restablish the situation.
However, BAA was confident. At the Queen's inauguration, the new facility was described as the "state-of-the-art" that was going to end the worsening experience of passengers in Heathrow. Heathrow's owner, BAA, said it expected the new baggage system at T5 to work "perfectly". It was needed as the competition is reinforcing. The new treaty agreement of open skies between the US and UK is likely to trigger a new price war as the market of transatlantic flights deregulates.
According to the Guardian, "a price war is already under way due to the intense competition between the three carriers that operate the Heathrow to New York route: BA, Virgin Atlantic and American Airlines. However, US competitors Continental, Delta and Northwest are also among the carriers launching new Heathrow to New York routes. A total of 7,112 extra seats and 39 new flights a week will be added to the route between London's airports and New York, a rise of 6% on last year."
Therefore, as the British operator is still struggling to sort out the situation, it is wise to avoid Heathrow and to try to find out other ways around London. You can use other airlines than BA and fly from T1, 2, 3, 4 (and some BA flights for short-hauls, Singapore, Australia and Bangkok have not moved to T5 due to the chao - you can find which plane is departing from where on ba.com/Which terminal). And you can also view other operating companies in Stansted and Gatwick airport here.
Gatwick, in South London, offers a wide range of flights to Europe (BA to France, Budget airlines to Italy, Denmark...), Middle East (Emirates to Dubai... ), Asia and North America. The facility is much better (albeit the difficulty due to specific security mesures in UK airports) and there is a fast train linking the airport to London Victoria in 30 minutes (or a normal train in 40 minutes). Stansted, east, is mainly used for budget airlines (such as Ryan Air or Germanwings) but NYC is served by American Airlines. Lutton, north of London, serves also more than 30 international destination including Africa. Eventually you can also use City Airport, close to Canary Wharf (the new business center in London) but with smaller airplanes and short-hauls.
When transiting, avoid London and especially Heathrow and prefer hubs such as Paris, Amsterdam or Frankfurt. In order to find more information on flights around the world, updated daily, you should subscribe to www.oagflights.com (annual £99 - €130).
Have a good trip ! :-)