Well.. if you live within the Doha City limits, Al Rayyan and Gulf Driving school would be good for you. But if you can make the extra trip to Abu Hamour, i recommend the Karwa Driving School. The instructors there are really professional, the don't take money from their students and are easy to talk to.

For Karwa, When it comes to the road test, it will be done around the industrial area, so less cars, therefore less hassle.

I don't believe it is easier to pass in one school than the other, it all really depends on the student drivers ability.

Good Luck. Cheers!