I'm taking a couple of trips in February 2016 and the cheapest flights I've found go through New Delhi. I wound up with a few different options which meant booking nearly all my flights through separate airlines on separate bookings. I know a transit visa is required to go through Customs to get checked baggage and go back through to your next flight.
Is going through Customs required if you have no checked luggage, only carry ons?
The three airlines I will be using through New Delhi are Emirates, Southern China Air, and either India Air or IndiGo (to go to Kathmandu, haven't purchased this ticket yet). All my layovers will be in the 2-6hr range. Obviously if I have to go through Customs I will have to extend my shorter layovers, but I hope that is not the case and I am able to do gate check-in for each airline.