If you look at an exercise in terms of most muscle used or stimulated or both, knowing that both the largest group and number of muscles are in fact in the back, then the machine pullover becomes a very important exercise for this reason alone.
And although, this is my opinion, the dip still requires the use of the back, the pullover by its sheer design, works the upper and lower torso through an incredible range of motion, whilst still using to a degree, the abs, pecs, biceps, triceps.
Machine Pullover for the win.
If you are a member of a fitness first, use the pullover, but use it properly for best results.
It's the second best exercise there next to the squat rack, which both are normally unused, or not used properly.