Understanding NMR Spectroscopy is, I think, the resolution of this dilemma. Keeler’s text is clear, describing the physical basis of NMR in a straightforward way that should work for just about any student. He handles the necessary quantum mechanics and operator representations with a deft touch that makes their mathematical derivations clear without producing an intimidating morass of equations. Naturally, some detail and rigor is swept under the rug in this approach, and an advancing student will want the Cavanagh book or Levitt’s Spin Dynamics to get a firmer grasp of the nuts and bolts, but as an introduction to the theoretical underpinnings Understanding NMR Spectroscopy is superb. Keeler’s explanation of relaxation processes is also excellent, and includes perhaps the best physical description of T2 relaxation I have ever read. The book also includes a useful little chapter on the workings of an NMR spectrometer that, while nothing special on its own, is also a good resource for an early-career grad student or rotator. Exercises at the end of each chapter can also be a good teaching tool (although, since the answers are available at spectroscopyNOW, not appropriate for a course).
Although the book is not explicitly oriented towards biomolecular NMR, it has a strong focus on heteronuclear experiments that ensures the information presented is appropriate for students interested in biomolecules.
I can’t praise this book without reservation, however. Some topics that might be considered important are glossed over or skipped entirely — chemical exchange, for example is barely mentioned, and REX not at all. Residual dipolar couplings are not discussed, and the angular dependence of the dipolar interaction is only skimmed. Chapters 10 and 11 are poorly structured and include inadequate and possibly confusing discussions of raising and lowering operators, coherence order, and coherence transfer pathways and diagrams. The mentor will need to take an active hand in explaining just what is going on in these sections.
That said, I think that Understanding NMR Spectroscopy will be an excellent book for grad students just starting out in biomolecular NMR or possibly rotating students who want a glimpse of the nuts and bolts of NMR theory. The gap between Derome/Claridge and Cavanagh has been pretty neatly filled by this affordable little volume ($40 at Amazon).