There are different locations that the manufacturer might love to put the engine of a particular car that he is trying to make. The engine can either be at the rear, middle or front. Now they have different advantages. If a vehicle has its engine in the rear, it is a rear engine placed car and this is the method that the Volkswagen beetle used in selling its product way back and even got the award of the best-selling car of all time - VW BEETLE. I would sincerely tell you a good advantage and a great disadvantage also. For rear engine vehicles, it has good grip and power unit and the drive can be all one assembly all due to the fact that the weight is placed on the rear wheels. The disadvantage of this particular type of car is that there is no much room for bags and luggage, another technical challenge is handling and this is affected because of less weight on the steered wheels. This type of cars mostly use flat type engines as the most common choice for manufacturing them.
Some vehicles have their engines at the front, in the past years, many cars with front engines were actually rear wheel drive cars and this was used for many years but yet still some manufacturers like the BMW still use this pattern of placing engines in their cars. The main feature in this type of cars is the long propeller shaft from the gearbox to the final drive which is part of the rear axle. The propeller shaft has some universal joints to allow for the suspension movement. There are some advantages of this type of positioning in which some are that the weight transfers to the rear driving wheels when accelerating, complicated constant velocity joints such as used by front wheel drive vehicles are not needed.
In a four wheel drive system, it all becomes a combination of all the good points mentioned above but does make the vehicle very much complicated and expensive. The main difference with four wheel drive system is that there is a transfer case which is needed to link the front and rear wheel. Vehicles with engines at the front is at an edge in any case of front end collision, the engine cooling is easier due to the air flow, since the weight is acting on the front, to enter a corner is easier, there is also more room in the passenger compartment, if the engine is mounted transversely, it aids the front wheel drive
Positioning of Engines in the middle is also a type of engine positioning. This has a major disadvantage in the space it takes in the vehicle, but in this, the weight distribution along the vehicle is good. This makes it the choice of high performance vehicle designers.