The rotational arm is a commonly used arm especially when a linear lift is not needed. A rotational arm is a simple arm that moves up and down. This arm is easy to make, but it cannot go as high as the other arms nor does it have a linear lift.
A 6 Bar is a really commonly used lift because of its great height and linear motion. This lift can lift higher than the rotational arm and can lift higher through the addition of more bars. However, when making a 6 bar you must keep all parallel distances between linkages equal. The linkages must also be sturdy and tight, but should still remain fiction less otherwise the arm will become really wobbly or so tight that it cannot move.