2-post vs 4-post -
The entire area under the car is accessible.
The lift has to be anchored to the floor, and may require the floor be reinforced to support the weight.
The car is always picked up by the frame, with the suspension hanging.
Care must be taken to determine placement of the lifting arms to keep the load balanced.
Ramps may restrict access to rocker areas.
The lift can remain portable - no anchoring required and many come with wheel sets - could be rolled outside if desired.
The lift picks up the car by its wheels, but jacking trays allow the car to be jacked up by the frame as well.
No arms to move, just drive on.
Can also be used for car storage (I suppose you could store a car on a 2 post, but don't know anybody that does).