I've been to both and here are my thoughts:
Shanghai is bigger than Mumbai
Shanghai has a higher population than Mumbai
Shanghai is more developed and 'flashy' than Mumbai
There's more to see in Shanghai
Shanghai has a higher GDP per capita than Mumbai
Shanghai has fewer homeless people/...
Tokyo is the world's largest city by size
Hong Kong has the biggest rich-poor divide in the world
Shanghai has the highest population
Mumbai is supposedly the most expensive city in Asia
Singapore????