Rigidbody Enemy and Collisions

Ok, I'm making a platformer game. My enemies have rigidbodys attached to them. I'm directly controlling their velocity by accessing the rigidbody.velocity component. The problem is, when I have them chase me, they don't run into things and stop. I want them to hit other rigidbodys and try to push against them, but go no where. Do I need to use AddForce? Will AddForce with the VelocityChange force type give me enough control? Thanks for the help! P.S UnityScript ;) Link to the *long* script https://dl.dropboxusercontent.com/u/33872519/Rigidbody%20Enemy%20and%20Collisions/EnemyScript.js