Malls are placed in various corners of Doha and as stated by vignale, people will drive to any of them. It really depends on your brand in order to select the correct mall location. (hard to get space though)... Generally, the middle class and high disposable income earners go to Royal Plaza and shop at sections of Villagio.

Would not bother considering City Center, Hayatt and The Mall if you are targeting high disposable spending customers and not the mass so to speak