  Hund's pairing refers to Cooper pairing generated by onsite interactions that
become attractive due to large Hund's exchange $J$. This is possible in
multiorbital systems even when all local bare interactions are repulsive, since
attraction in specific channels are given by certain linear combinations of
interaction parameters. On the other hand, pairing processes such as the
exchange of spin fluctuations, are also present. We compare these two
mechanisms on an equal footing using electronic bands appropriate for different
classes of multiorbital systems over a wide range of interaction parameters. We
find that for systems without clear nesting features, the superconducting state
generated by the Hund's mechanism agrees well with that from the full
fluctuation exchange vertex when Hund's exchange and spin-orbit coupling are
sufficiently large. On the other hand, for systems characterized by a peaked
finite-momentum particle-hole susceptibility, spin-fluctuation pairing
generally dominates over Hund's pairing. We conclude that Hund's pairing states
are unlikely to be realized in systems like Sr$_2$RuO$_4$ and generic
iron-based superconductors.
