Kolkata is nice, I have to say Delhi is less appealing as I do think it's a little more intense and cluttered and polluted than some of the others. I'd have suggested Mumbai, with some nice sights, as well as pretty good mix of Indian and international cuisine and night life.
Oh, but Hyderabad would've been much harder to handle than Delhi, I semi-live here (HYD), lovely city but it's intense. However if you like craft beer this is the place to be, lots of microbreweries that have popped up in recent years.