Which one is the right answer?
Not before you have committed — that part is the bit worth doing yourself. What I can do is make sure you have what you need.
Skill-based routing needs three things in place before it will assign anything: a rating model that defines the scale, the skills themselves attached to representatives at some proficiency on that scale, and a work classification ruleset that decides which skill a conversation demands. Miss any one and conversations fall through to the default queue.
So what does the rating model actually do?
It is the scale everything else is measured on — say 1 to 10, or Beginner to Expert. A skill on its own says a representative speaks Spanish; the rating model is what lets the system prefer somebody who speaks it at 9 over somebody at 4 when both are free.
“Skill-based routing requires a rating model that defines the scale used to measure agent proficiency.”
Source
Configure routing rules and skill-based routing
The tutor answers from the unit the question was written from — and says so when the material does not cover it, rather than inventing something.