I'd say Iwakuma was more stable in pitching in the games of last WBC.

You have to be physically tough to survive a whole major league season so Iwakuma's
right shoulder that was not so tough can be his weak point.
Darvish's more physically strong than Iwakuma.

Darvish has potential to win more than 18 games but let's not be so
optimisitic because this is his frist season in MLB. I'd say he'll win 15 or more.
This is sure because Kuroda, former a Dodger and currently a Yankee, could win 13 last season.

Without injury, Iwakuma has potential to win more than 12 games.