  Motivated by the large body of literature around the phenomenological
properties of accreting black hole (BH) and neutron star (NS) X-ray binaries in
the radio:X-ray luminosity plane, we carry out a comparative regression
analysis on 36 BHs and 41 NSs in hard X-ray states, with data over 7 dex in
X-ray luminosity for both. The BHs follow a radio to X-ray (logarithmic)
luminosity relation with slope $\beta=0.59\pm0.02$, consistent with the NSs'
slope ($\beta=0.44^{+0.05}_{-0.04}$) within 2.5$\sigma$. The best-fitting
intercept for the BHs significantly exceeds that for the NSs, cementing BHs as
more radio loud, by a factor $\sim$22. \This discrepancy can not be fully
accounted for by the mass or bolometric correction gap, nor by the NS boundary
layer contribution to the X-rays, and is likely to reflect physical differences
in the accretion flow efficiency, or the jet powering mechanism. Once
importance sampling is implemented to account for the different luminosity
distributions, the slopes of the non-pulsating and pulsating NS subsamples are
formally inconsistent ($>3\sigma$), unless the transitional millisecond pulsars
(whose incoherent radio emission mechanism is not firmly established) are
excluded from the analysis. We confirm the lack of a robust partitioning of the
BH data set into separate luminosity tracks.
