I really liked Mumbai, and would love to visit that city again under better personal circumstances. It was the most different place I've been, culturally, from my own background, and I learned a lot while there. I was awed at the size of the city, even though I spent much of my childhood living in big cities and have lived in NYC for 11 years. Mumbai just seemed futuristic in how endless it was. And that sort of futuristic vibe was contrasted with how ancient the city was. I love history and the juxtaposition of the historic and the modern (this is also what I loved about Cairo and Puebla City).
The diversity of the population was also a wonderful aspect, because I got to meet a lot of people from a lot of different cultures; Indians from all over the country, as well as some foreign expats. Though I speak no Hindi, nor any of the other many languages native to India, it wasn't at all a hinderance, since so many Indians speak English (I also really enjoyed learning some of the quirks of Indian English). The only time I had to use another language besides English was when I had tea with a couple of African tourists who spoke French.
Here's one of my favorite pictures of me in Mumbai:
Other than Mumbai I quite enjoyed Puebla City. Mexico is a beautiful and culturally rich country, and I think few tourists penetrate deep enough. I'd like to visit Cairo again, though I admit that Egypt was the only country where I felt a tinge of concern for my safety (specifically, as a woman), not in Cairo, mind you, but outside the city.