  We show that at higher frequencies, and thus higher axion masses,
single-photon detectors become competitive and ultimately favored, when
compared to quantum-limited linear amplifiers, as the detector technology in
microwave cavity experimental searches for galactic halo dark matter axions.
The cross-over point in this comparison is of order 10 GHz ($\sim 40\ \mu$eV),
not far above the frequencies of current searches.
