Relatively new big leaguers? Neither is a nibbler, both are confident in their stuff, and they're not afraid to go after batters.
Dobbins leads all Sox starters in lowest BB9 at 1.4. Next is Buehler 2.4, and Fitts 2.6.
The rest of the rotation: Giolito 2.7, Crochet 3.0, Newcomb 3.3, Houck 3.5, and Bello 5.5 (really?).