The two different types of six-cylinder engines are the straight-six and V6 engines. The main difference between the two is the way in which the cylinders are organized.
Straight-six cylinder engines consist of six cylinders lined up in a row vertically, making it inherently balanced. Straight-six cylinder engines are considered to be the smoothest engines in existence due to their layout and firing order. The engine's simple design leads to a low manufacturing cost and also makes it easy to work on, similar to an inline four cylinder engine. Straight-six engines are often difficult to package and have more rigidity than a V6 due its long and narrow design. Straight-six engines also have a high center of gravity and are not ideal for front wheel drive vehicles.
V6 engines have six cylinders total, but the cylinders are arranged in two three-cylinder columns that are lined up next to each other. V6 engines allow for greater displacement than four cylinder engines which allows for more power. V6 engines are also more compact than straight-six engines and can easily be used in front wheel and rear wheel drive cars. V6 engines have a high center of gravity similar to straight-six engines, but V6 engines often cost more. V6 engines also add more weight to the vehicle due to two extra exhaust manifolds and a secondary imbalance puts more weight on the crankshaft.