In Pakistan there are many christians whose muslim ancestors kept their muslim names even after converting to christianity. So today in Karachi i have friends like Shaun Khursheed and Aashir Aziz. That way we can say Khursheed and Aziz are common surnames too.
Most of them didn't convert from Islam but from low caste Hindus, Punjabis and Sindhis were all once Hindu before they converted to Islam and other religions, same way Pashtuns and Balochis were once Zoroastrian before they converted to Buddhism (improved version of Hinduism) at the hands of Indian missionaries and then to Islam.
Christians and Hindus in Pakistan adopt Arabic names to fit in. Brother Muhammed Yusuf was Yusuf Yohanna before converting to Islam and even then both his names were Arabic and common Muslim names.
Khursheed and Aziz are not ancestral or family names, they are Arabic first names, in some Pakistani cultures instead of giving their child the family name they just give him (or her) his fathers first name as a surname.
I think the most common surname has to be Khan and I hate it, Pakis often associate it with Pashtuns but it's originally a Mongolian title and means "leader", lots of other cultures adopted it and now it's used all over Asia amongst Mongolians, Arabs, Punjabis, Pashtuns, Turks, you name it.
It's too common, I'm changing my surname to Durrani (my tribe name) or one of its off shoots (Popalzai etc.) in my paternal lineage.
among christians..umm...Brown, Williams, Jones, smith among hindus..singh..dont know much among muslims..khan as most of the ppl said it b4 and shah..i think and i thnk ahmed is common as well..hai na!