NMR spin diffusion experiments have the potential to provide both resonance assignment and internuclear distances for protein structure determination in oriented solid-state NMR. In this paper, we compared the efficiencies of three spin diffusion experiments: proton-driven spin diffusion (PDSD), cross-relaxation-driven spin diffusion (CRDSD), and proton-mediated proton transfer (PMPT). As model systems for oriented proteins, we used single crystals of N-acetyl-L-N-15-leucine (NAL) and N-acetyl-L-N-15-valyl-L-N-15-leucine (NAVL) to probe long and short distances, respectively. We demonstrate that, for short N-15/N-15 distances such as those found in NAVL (3.3 A), the PDSD mechanism gives the most intense cross-peaks, while, for longer distances (>6.5 A), the CRDSD and PMPT experiments are more efficient. The PDSD was highly inefficient for transferring magnetization across distances greater than 6.5 A (NAL crystal sample), due to small N-15/N-15 dipolar couplings (<4.5 Hz). Interestingly, the mismatched Hartmann-Hahn condition present in the PMPT experiment gave more intense cross-peaks for lower H-1 and N-15 RF spinlock amplitudes (32 and 17 kHz, respectively) rather than higher values (55 and 50 kHz), suggesting a more complex magnetization transfer mechanism. Numerical simulations are in good agreement with the experimental findings, suggesting a combined PMPT and CRDSD effect. We conclude that, in order to assign SLF spectra and measure short-and long-range distances, the combined use of homonuclear correlation spectra, such as the ones surveyed in this work, are necessary.