  We investigate how the total radio luminosity of AGN-powered radio sources
depends on their accretion luminosity and the central black hole mass. Our
studies cover about seven orders of magnitude in accretion luminosity and the
full range of AGN black hole masses. We find that AGNs form two distinct and
well separated sequences on the radio-loudness -- Eddington-ratio plane. The
`upper' sequence is formed by radio selected AGNs, the `lower' sequence
contains mainly optically selected objects. Whereas an apparent `gap' between
the two sequences may be an artifact of selection effects, the sequences
themselves mark the real upper bounds of radio-loudness of two distinct
populations of AGNs: those hosted respectively by elliptical and disk galaxies.
Both sequences show the same dependence of the radio-loudness on the Eddington
ratio (an increase with decreasing Eddington ratio), which suggests that the
normalization of this dependence is determined by the black hole spin. This
implies that central black holes in giant elliptical galaxies have (on average)
much larger spins than black holes in spiral/disc galaxies. This
galaxy-morphology related radio-dichotomy breaks down at high accretion rates
where the dominant fraction of luminous quasars hosted by elliptical galaxies
is radio quiet. This led to speculations in the literature that formation of
powerful jets at high accretion rates is intermittent and related to switches
between two disk accretion modes, as directly observed in some BH X-ray
binaries. We argue that such intermittency can be reconciled with the spin
paradigm, provided that successful formation of relativistic jets by rotating
black holes requires collimation by MHD outflows from accretion disks.
