On pure performance, probably Kamran, his keeping was bad, and his batting average even for a wicketkeeper let alone one picked mainly for his batting was poor. Though I guess you can argue that there were few options.
Asad's record isn't exactly terrible, it's not 20s, but pretty mediocre. But he was playing at 6 a position you often groom a youngster, with strong middle order bats in Misbah, YK, even Azhar. And yet never 10 year of consistent test chances without being dropped. Pretty sure we could have picked a middle order bat at 6 who would have done better with those chances, even if there was a lack of batting talent in Pakistan. And that golden opportunity to be able to improve under batting with very good, experienced test batsmen in Misbah and YK has been wasted now.