First GAT = LGW.
You don't say were your flying from but Virgin also fly into LGW from Boston.
LHR is about 15/20 miles outside Central London (normally measured from Charing Cross). It is linked to London by Rail to Paddington, Tube into Central London, many buses and the M4 motorway.
Gatwick is a little further out, but has excellent rail links to Victoria (30 mins) and is close to the M23 which links into the M25 London orbital.
Stansted (STN) (no 'a') is about 40 miles from central London. It also now has good rail links into Liverpool Street (45 mins) in the financial centre of London (trains every 15 minutes). It is also close to the M11 motorway, which as long as it is not being dug up, links well with the M25 and other London roads.
There are also buses which link all three airports.
Assuming you are coming from the states, why not try something different and fly EL AL into Stansted from NY??
Hope thats useful.
L1011 - P F M