An update may be in order...

I stayed at the Hilton Janakpuri as per keyser's recommendation. My pre-paid (non airconditioned) taxi took about 25 mins to the hotel in the afternoon and the cost was just 320 INR. As Hhonors Gold I was upgraded to the executive floor with a pool view. The lounge was great and I had a good rate although they apply a strange fixed luxury tax of 1300 INR instead of (the standard?) 10%.

Some words of warning though. The hotel does not accept Diners Club even though I had used it at hhonors.com to book the prepaid room. They then charged my Visa in Euros with their own currency transaction fee/rate without my permission. No biggie, but anyway! Going back I made the mistake of accepting the "hotel taxi" instead of e.g. Meru cabs. Of course the meter "broke down" on the way to the airport. I paid a flat fee of 500 INR which is of course still ok. The taxi driver appeared very pleased. The ride to the airport in morning traffic took about an hour and in very bad traffic it might become a real problem to catch your flight in time.

You could also take the metro to the airport (involving one change of trains) but I have no experience of that.

The Janakpuri Hilton is like a new Hilton anywhere; a contrast e.g. to the Mumbai Hilton which is a very old-fashioned ex-Le Meridien.