I have done both, and at the moment I own car/s. There are pros and cons of both the options.
There are many factors to consider.
1. How long you are planning to stay here? if it is more than one/two years, then I would buy a vehicle.
2. Rental. For an example you may have to pay around AED2500-3000 monthly (rental may be lesser for yearly contracts) for a Toyota Camry from one of the main operators. If you opt to buy the same car (with few years' loan) you would pay a lesser monthly installment. However, if you rent, you would be able to drive latest models every year without bothering for servicing those etc.
3.If you like a particular vehicle, your time in the UAE may be the best time to buy it and enjoy.
4. Buying:if you opt to a brand new car, you know where to go. Most of the time there are various "offers", for an example, free service for xx number of years/up to xxxxxxkm. For financing, there may be bank representatives stationed in the Car Showrooms.
If you opt to buy a used car, most dealerships (e.g. AGMC-BMW, Al Tayer- Ford, Lincoln; Al Futtaim- Toyota, Honda, Al Rostamani-Nissan, Renault etc) have pre owned car section(usually their prices are higher). There are other dealers and you can opt to check on GN or Dubizzle website for advertisements.
5.Selling the car can be done in many ways, the dealerships buy some of the vehicles back, there are companies who buy used cars. However, both the aforesaid options may not offer you a good price. You may opt to sell it advertising on websites like Dubizzle or GN.
All the best.