If you are renewing 'personal' car not 'company' car then you can go to almost anywhere.

Madinat Khalifa is popular - this means it will take a looooong time when you get there. I have used the Traffic Division at Rayaan, and the Traffic Police at Mamoora (the one next to the vegetable market) - it took me less than 5 minutes on each occassion.

Good luck to you sir!
:-)