I feel that if a three position is available that the three position is the best buy. Manufacturers are making multi-position heads that are basically three position trinoculars with the ability to accept two or more cameras. These can be quite useful if you need them. They can make the microscope look quite top heavy however. Sometimes a support stand for one of the cameras will be needed.
Some heads take the reversed image that all biology people know and correct it.
This means that when the stage is moved left the image moves left. This is how all heads should be. These heads are found in industry were their higher cost is justified by their ease of use. Industry also pioneered the Ergo head. Invented by Leitz the Ergo head lets the user adjust the angle of the head to suit there needs.