From Regents park you can easily get to the Piccaddily line tube for trains to Heathrow, or go across to Paddington and take the Heathrow Express, but at a cost of £15 compared to £3.40(?) for the underground.

Easyjet at Luton requires, I believe a train ride and then a shuttle bus to the airport. Alternatively you could take coach. There is a special easyjet fare of £8 return at www.greenline.co.uk and the nearest pick up point to you seems to be Baker Street Station. Journey time is about 90 minutes, but easyjet is notorious for it's cut off times. Miss it and pay to get on the next flight.

Personally, I'd take BMI from Heathrow. Why pay the same price for a discount no frills airline when you can pay the same for a full service one? Not getting food for a 1 hour flight may be a small thing, but having to scramble for a seat is just so uncivilised. Sorry, but it just is!