  I have been asked to make the case here that CHDM is the best theory of
cosmic structure formation, and indeed I believe that it is the best of all
those I have considered if the cosmological matter density is near critical and
if the expansion rate is not too large (i.e. $h \equiv H_0/(100 \kmsMpc) \lsim
0.6$). I discuss CHDM together with its chief competitor among CDM variants,
low-$\Omega_0$ CDM with a cosmological constant ($\Lambda$CDM). $\Lambda$CDM
with $\Omega_0 \sim 0.3$ has the possible virtue of allowing a higher expansion
rate H_0 for a given cosmic age t_0, but the defect of predicting too much
fluctuation power on small scales. Also, except for the $H_0-t_0$ problem,
there is not a shred of evidence in favor of a nonzero cosmological constant,
only increasingly stringent observational upper bounds on it. CHDM has less
power on small scales, in good agreement with data, although it remains to be
seen whether it predicts early enough galaxy formation to be compatible with
the latest high-redshift data. I also briefly compare CHDM to other CDM
variants such as Warm Dark Matter (WDM) and tilted CDM. CHDM has the advantage
among $\Omega=1$ CDM-type models of requiring little or no tilt, which appears
to be an advantage in fitting recent small-angle CMB anisotropy data. The
presence of a hot component that clusters less than cold dark matter lowers the
effective $\Omega_0$ that would be measured on small scales, which appears to
be in accord with observations, and it may also avoid the discrepancy between
the high central density of dark matter halos from CDM simulations compared to
evidence from rotation curves of dwarf spiral galaxies.
