In QMs, the body has two bases: the anterior (the arms) and the posterior (the legs). They can be turned into mixed bases, lateral (arm and leg of the same side) or diagonal (arm and leg of opposite side).
The action of the arms is principally pushing (up or down), and only rarely in a mix of pushing and pulling. The triceps and shoulder muscles are particularly important in these moves. A complementary form of movement would be climbing, which involves primarily pulling.
Let us consider first the position and flexion of the limbs. The arms and legs can be straight or flexed to various degrees, but it is also important to keep in mind the relative position of the main joint (hip, shoulder) to the point of contact on hand and foot. The square pose, where the joint rests vertically above the hand or foot allows to go through all degrees of flexion of the limbs without moving hand or foot.
Another interesting posture is "pointed", where the limbs from each side of the body are slightly oblique, in front and behind the joint, making a triangular base. These pointed bases are both stable and well suited for motion, but they don't allow as much variation in flexion.
Both postures of the limbs, square and pointed, are good to offer relative rest. Depending on the amount of flexion and the distribution of weight between the weaker (arms) and stronger (legs) limbs, those can be more or less restful.