Of course, Karachi. You will feel the power of the Pakistani navy when you are in Karachi. There is nothing similar in Dhaka. You will only find garbage and traffic in Dhaka, while Karachi is beautiful. Not to mention that Dhaka is one of the top polluted cities in the world
Karachi has its polluted spots just like Dhaka.
Difference is that Dhaka is getting cleaner in relative terms as it is pulling down lots of slums and replacing them with apartment blocks - it is coming from a very low base and so easier to do. Also a lot of sanitation infrastructure is getting put in.
Dhaka has more congestion for sure but let us see how the metro lines being built and the bypass infrastructure being built leads to a reduction in this area - it will take many years before this can be assessed.