After having read both a couple of times cover to cover (through the course of residency/fellowship), I definitely favor Gabbe for several reasons: 1) it is an easier read, 2) it covers basic, normal pregnancy better, and 3) there is no specific focus on the "Parkland way." The latter is an important and fantastic item, has contributed greatly to our field, but is not always congruent with how obstetrics is practiced outside of UTSW.
Best of luck on the rotation.