I have rented vehicles in Lahore quite a few times for short term and long term. I tried several car rental agencies and found Hertz in global and PSG Rent a Car in local companies as one of the best service provider in Lahore. There vehicles are all latest and fully insured.
The good thing is you can also rent vehicle on self drive and save a valuable seat specially when going with friends or family on long road trips in northern areas of Pakistan. Here's the link http://www.pakrentacar.pk