How many reports has the BMC sponsored Mr. Riaz?
Did BMC sponsor "Planet of the Slums" (ISBN: 1844670228) by Mike Davis too?
Read it and you'll know which city has a bigger slum population.
I have read it. The Davis book does not say that Orangi is bigger than Dharavi slum, nor does it compare the services available to residents, or their quality of life.
All it says that about half of Karachi population lives in various Katchi Abadis, which is less than the 60% of Mumbai residents living in slums.
You did not provide any links, but I'll give you the links to back up my statements:
Planet of slums - Google Books
Slums