Recently visited Varanasi and I very strongly recommend Roobaroo walks. Their ability to adapt to our diverse group (my mother, my 9 year old daughter and myself) and its needs ranging across fun, art, music, culture and religion, was outstanding.
Anupam, their story teller is very knowledgeable and hospitable. He made us feel completely at home.
I can say with a lot of conviction that one of the best ways to experience Varanasi would be to do it with Roobaroo walks.