There are 2 main types or styles of 2 post car hoists, the base type 2 post car hoist and the clear floor 2 post car hoist.
Base type 2 post car hoist
This type of car hoist is usually driven by twin hydraulic rams, one for each post. The older style and not as safe style is a screw type. The twin hydraulic rams push a heavy duty chain that is attached to the carriage and lifting arms in each post. This type of hoist is suitable for service work- changing oil, rotating tyres and inspections.
The disadvantage to a base type 2 post car hoist is the cover plate on the floor between the posts, this ranges in size and height, the smaller the better.
This cover plate protects and covers the hydraulic line and the equalising cables.
The advantage of a base type 2 post car hoist is you require less ceiling height, most of the posts are under 3m with a recommended ceiling height of 3.6m. 1.8m lift height and 1.8m for the vehicle, obviously sedans aren't this tall so your circumstances may be different depending on the vehicle/s you intend to work on.
Clear floor 2 post car hoist
Like the base type car hoist the clear floor is usually driven by twin hydraulic rams. The more advanced and modern clear floor hoists have full length direct drive rams, where the carriage is directly attached to the ram.
The big advantage to direct drive style is there are less moving parts, no chains, no pulleys so less maintenance and smoother operation. Clear floor car hoists are the most popular and are most common in workshops.
The reason being that the equalising cables and hydraulic hoses are carried overhead rather than across the floor. Giving you a "clear floor" to work with, hence the name.
You can use a clear floor hoist for all the things you can a base type plus transmissions, gearboxes, restoring old cars and anything other type of work where a jack would be used to manoeuvre components from the front to back of vehicle.
Ensure that whatever hoist you choose has Work Cover design registration and complies with AS1418.9.