Editor's note: Now that free agency has started, Keith Law picks out possible best values, worst values and trade targets across every position group. He started with the catcher position, followed that with corner infielders, middle infielders and outfielders, and now continues the annual series with a look at the starting pitchers who have hit free agency, as well as some potential trade targets.

For the top 50 free agents across every position, click here.

Top free agents

Zack Greinke, RHP: I had Greinke one spot ahead of Price in my main rankings, but I won't argue with anyone who says the two should be flipped; both are bona fide aces, both are immediate difference-makers for 2016, both have strong health histories and reasonable arguments that they'll maintain their levels of output for several years to come. I gave a slight nod to Greinke, even though he's two years older than Price, because his style of pitching depends so little on velocity and so much on changing speeds and locations, a pitching approach that should survive even as his velocity faces its inevitable age-related decline.

David Price, LHP: If you prefer power in your starting pitchers, you should favor Price over Greinke.