If you are going for a car in Qatar, Toyota stands out over all others. Toyota has the advantages that the spare parts are cheaper than other car brands, the cars have a resale value, and there are many parts where you can find non-original ones (locally known as "tejari"). Also, even original spares can be purchased from several outlets and not just from the agents.
Next in line is the Nissan. You can go for any of the models. It too has a market value but lower to that of Toyota. Try to avoid Mitsubishi as the spare parts are costly and most of them are available with just the agents. Mitsubishi does not have a good resale value.
If you know about cars or know of a good mechanic, you can go for a second-hand car. Keep in mind buying a second-hand car from unknown sources is always a blind-buy. People won't tell you of the problems of the car they are selling out. This is especially true with second-hand car dealers. It is advisable to buy one from someone who is leaving Qatar for good especially if he has been the first owner of the vehicle.
Trust this helps.