Hummm. I can speak for my DD and say that for her depth is easy. She can go over something once and just get it. She HATES going over something time and again. For example; math. She hated Saxon and all the reviews. She loves Singapore and flies through it.
So all that said I believe that mastery of the main subjects is the most important objective. We don't, IMO, have to cover every subject because our children have a lifetime of learning ahead of them.
I follow most of The Latin-Centered Curriculum and supplement with some WTM. When neither of those guides work I go to Charlotte Mason. This combination, for me, keeps things simple but provided a solid education that fits my child just right :D