Depends on your budget and number of days you want. there is a hotel/ resort above Shimla. which is expensive but number one honeymoon resort in Asia, as claimed by an article I read, a while ago. wild flower is the name, I guess.
Auli is the best honeymoon destination to visit in Northern part of India. It is in Uttrakhand and is easily reachable by volvo bus. If you can, then try visiting North Eastern side of India which has places like Sikkim and Shilong.
Since its month of may try a cool destination...!
shimala and kullu manali are crowded and popular destinations these days...
Auli is superb if u love adventure....
One of the most unexplored part of India and hence wonderful is North East...
visit Sikkim... i personally feel this place is Singapore for Indians...
happy travelling ;):)