Depends upon the daily usage and how much longer you want to keep it.
Go for Mehran (if want to use within city) - try to get as much as latest model as you can
Go for Margalla (Maintenance would be a bit costly, CNG and Patrol consumption would be a bit high due to 1300 Cc engine) but it has more space, good seating & drive, good suspension, can take outside city on highways easily if well maintained.