  We investigate quark flavor signals in three different supersymmetric models,
the minimal supergravity, the SU(5) SUSY GUT with right handed neutrinos, and
the minimal supersymmetric standard model with U(2) flavor symmetry, in order
to study physics potential of the present and future $B$ factories. We evaluate
CP asymmetries in various B decay modes, $\Delta m_{B_s}$, $\Delta m_{B_d}$,
and $\epsilon_K$. The allowed regions of the CP asymmetry in $B\to J/\psi K_S$
and $\Delta m_{B_s}/\Delta m_{B_d}$ are different for the three models so that
precise determinations of these observables in near future experiments are
useful to distinguish the three models. We also investigate possible deviations
from the standard model predictions of CP asymmetries in other B decay modes.
In particular, a large deviation is possible for the U(2) model. The
consistency check of the unitarity triangle including $B\to
\pi\pi,\rho\pi,D^{(*)}K^{(*)},D^{(*)}\pi,D^{*}\rho$, and so on, at future high
luminosity $e^+e^-$ $B$ factories and hadronic $B$ experiments is therefore
important to distinguish flavor structures of different supersymmetric models.
