I think the Taj on Maan SIngh Road is a great location. You can walk to some attractions (India Gate, Lodhi Garden, Gandhi Smitri House, Gallery of Modern Art, National Museum) and the Khan Market Metro is very close which makes a trip to Connaught Place easy. It's not far from the Hazrat Nizzamddin Railway station which is the best station for a trip to Agra. Oberoi would also be a great place to stay, and closer to Nizzamuddin station. I'd forget about Marriott or Hilton points and just stay in some very luxurious Indian hotels like Taj or Oberoi.