The most common roots for skills are Perception, Will and Agility. Why? Because that is the kind of creature that human beings are; we use our insight, empathy and manual dexterity to solve problems.
Create some Giant life paths, and I could see Power and Forte making a lot of appearances in their specialized skills—applying their advantages in that area in specific ways that would pretty well kill other stocks.
Likewise, centaurs would probably have more Speed and Forte rooted skills.