I thought of a third approach.
If you had a hooked conveyor belt on a pivot in the body, which was on rails, you could lift yourself from the ground, tilt the pivot to grasp the second rung, then elevate yourself above the first rung and hang from the second. Repeat to hang from the third rung.
Here's a picture:
http://imgur.com/w37qr
It would then repeat this to get up to the third ring.
Pros:- Doesn't take as many motors
- Robot does not have to be specifically designed to lift.
Cons:-Takes a long time
-Requires a functioning hooked conveyor that can lift the whole robot