I'm a city owner and am pretty much satisfied with my vehicle. Here is an honest analysis of both cars
Comfort: Both have excellent comfort levels with ample leg space both in the front and at the back, however, GLI has more width and has arm rests.
Interior Quality: The interior of both vehicles is highly inferior with low grade plastic. It all comes down to personal preference of which colour you want to choose. Some people prefer beige whereas others are content with black.
Suspension: City has a stiffer suspension whereas the gli has a slightly softer suspension making the drive quality comfortable on bumpier roads, especially in the rural areas.
Pick up: City's pick up is awesome and the drive quality is sporty whereas GLI is a tad sluggish due to an underpowered engine (the same that is being used on the BELTA) for such a heavy body.
Body strength and durability: Corolla wins hands down when it comes to body strength and durability
Mileage: Both cars have excellent mileage and will give you anywhere around 12-14 km/l in city and 16-18 km/l on motorway subject to driving style and conditions.
Conslusion: City is a good economical choice if you commute on the motorway between big cities such Lahore and Islamabad. If you are a frequent traveler to rural areas, then Corolla is the ideal choice because of its durability and slightly higher road clearance.
Being a City owner myself, and judging by the options you're planning to consider, I would seriously advise you to buy Corolla. Increasing City's suspension will ruin its drive quality. Mileage is not a issue. Both cars have excellent mileage.