Sheppard all the way. Used it for CFI,II
No gimmicks, no extensive reading. They tell you this on day 1.
You get a limited number of questions from an updated database, which is a major plus. Study that and you pass. Simple as that.
For detailed explanations you have an unlimited number of resources on your hand, and ofcourse your instructor.
If your goal is to PASS a written in minimum time with excellent customer service (even at 2 am), Sheppard is the way to go.