In my honest opinion, I really don't understand what Premium cars are all about, especially since you have to almost double your cost by adding in the options!
The more options you have, the more ways it could go wrong, and given the picture about the dealerships as painted by Xulfiqar, expect a scary bill as well as bad workmanship. Shah Nawaz is probably the oldest in this business in Pakistan, and Dewan has been keeping customer's money and delaying delivery of BMWs by upto a year, I guess your choice for brand of car is narrowed down by the people representing it in Pakistan, and I would hence second Xulfiqar and go for Mercedes.