I wouldn't tip at all.

I gave the bellman a tip when shown to my room at the ITC Maurya Delhi a few weeks ago. He was quite shocked.

Then we moved to the Meridian in Delhi and the kindly bellman was gone before I could even get my hand into my pocket. Our luggage was delivered by a guy who (contrary to US approach) did not hang around waiting for a tip but just left.

So, I asked some of the Indian guests at the Meridian about tipping and was told it was not done.

Then, went on a tour to the Taj Mahal where it was obvious neither the driver or guide were expecting a tip.

So, as far as I can tell it just isn't an Indian thing.