It's a tough call for fantasy. Both pitchers have improved in a relatively steady manner, but Beckett had one hiccup.
Beckett had HR issues in '06:
Other than that, you're pretty much picking the same pitcher. Beckett strikes out a few more guys, but CC walks a few less. The fact that Beckett has faltered once while CC hasn't has me leaning toward CC as the guy I'd take if I had to choose.
For real life, though, I'd take Beckett without looking back. One of the few assertions that I agreed with this post season was the claim that Beckett has become the new "big game" pitcher of this generation. The man flat out delivers when it matters, and if this post season was any example, CC does not.