Colin Gardens is in Hendon, nearest tube station is Hendon Central.
http://www.streetmap.co.uk/map.srf?x=521864&y=189018&z=110&sv=colin+gardens&st=6&tl=Map+of+Colin+Gardens,+London,+NW9&searchp=ids.srf&mapp=map.srf
As all London airports are outside the city, it really depends on where you can get the cheapest flight into as it will take at least an hour and a half to get there from any of the airports.
If you fly into Gatwick, get the Gatwick Express to Victoria. Then change for the underground, take the Victoria Line Northbound to Euston, change for the Northern Line northbound to Hendon Central. It's in zone 3 so make sure you have a ticket that covers zone 3. It should take you about 2 hours from the airport.
If you fly into Heathrow, take the Heathrow Express to Paddington, change for the tube. Take the Circle or Hammersmith and City line eastbound to Euston Square. Walk from Euston Square to Euston (about 5 mins walk) then get the Northern Line northbound to Hendon Central.
You can also take the Piccadilly Line from Heathrow if you have plenty of time. Change at Leicester Square for Northbound Northern Line to Hendon Central.
If you fly into Stansted, take the Stansted Express to Liverpool Street station, change for the Metropolitan, Hammersmith and City or Circle line Eastbound to Euston Square and change as above.
If you fly into Luton it will take a bit Longer but can still be done. Take the train from Luton Airport to Luton Airport Parkway and then from there to London St Pancras. Walk to Kings Cross and then get the Northern Line northbound to Hendon Central.
www.nationalrail.co.uk
www.tfl.gov.uk/journeyplanner