The Sunday Express have published the top 5 best tour operators for India, I personally don't use tour operators as I prefer to book everything myself but there are a lot of topics regarding this subject so thougt I'd post the Express findings.
1) Cox & Kings
2) Voyages Jules Verne
3) Hayes &Jarvis
4) Greaves Travel and Oberoi Hotel & Resorts
5) Treyn Holidays (Rail holidays in India)