Two wheel drive
Front wheel drive seems to be the option for many car manufacturers and with good reason.
Most cars have their engines in the front so to drive the front wheels seems a logical choice. The advantages of this system are that the distance between the engine and the driven wheels is shorter than in a rear wheel drive and there is less of a power loss due to mechanical inefficiency.
The production costs are lower because there are fewer parts and interior cabin space is maximised because there is no centre tunnel. The engine sitting over the driving wheels gives better traction.
The main disadvantage is that when the vehicle is accelerated the weight of the car shifts to the rear and the front wheels tend to scrabble for grip.
Rear wheel drive has an immediate advantage in that the rear wheels are driven and this is where the weight shifts on acceleration. A longer driveshaft to the rear wheels and the need for a rear differential add to the production costs.
The extra weight results in reduced efficiency.
Four wheel drive
4WD is commonly regarded in the motor trade as a vehicle with selectable four-wheel drive. That is, a vehicle that drives in two-wheel drive under normal conditions and has an option of selecting four-wheel drive for certain situations.
4WD usually refers to "off road" vehicles that have a high and low range selectable four-wheel drive with a centre differential lock up mechanism for those slippery conditions when the front and rear wheels are rotating at different speeds.
The low range has greater pulling power or torque and is used for climbing and pulling in off road situations. The high range is used in slippery situations like sand or snow.
AWD or all wheel drive differs from 4WD in that it is not selectable and there is no high and low range to choose from. This system is used in cars like the Subaru Imprezza and although it is called all wheel drive, the fact is that the front wheels are driven most of the time with the rear wheels only driven under certain conditions. Sensors monitors wheel slippage and if the front wheels begin to slip, like on hard acceleration from a standing start, the driving power is transferred to the rear wheels. This greatly enhances performance and handling in slippery conditions.
Any four-wheel drive system is expensive to produce, adds weight to the vehicle and running costs are higher.
If you are only doing one major four wheel drive trip per year it may be cheaper to fly to your destination and hire a vehicle there.