Passive walkers are robots that can produce a stable cyclical movement similar to walking on mildly inclined surfaces. In recent years, various investigations have been conducted on this subject. Since this is a new field of research, the effect of structural parameters on the movement of these walkers and the development of more human-like movement models can be further investigated. This paper compares three popular models for passive dynamic walkers: Garcia's mode, Wisse's model, and our own extended Wis-se's model with arm. Our research shows that the extended models lead to more energy efficient and stable walking.