  Single top quark cross section evaluations for the complete sets of
tree-level diagrams in the $e^+ e^-$, $e^- e^-$, $\gamma e$ and $\gamma \gamma$
modes of the next linear collider with unpolarized and polarized beams are
performed within the Standard Model and beyond. From comparison of all
possibilities we conclude that the process $\gamma_+ e^-_L \to e^- t \bar b$ is
extremely favoured due to large cross section, no $t \bar t$ background, high
degrees of beam polarization, and exceptional sensitivities to $V_{tb}$ and
anomalous $Wtb$ couplings. Similar reasons favour the process $e^- e^- \to e^-
\nu_e \bar t b$ for probing top quark properties despite a considerably lower
cross section. Less favourable are processes like $e^+ e^-, \gamma \gamma \to
e^- \nu_e t \bar b$. Three processes were chosen to probe their sensitivity to
anomalous $Wtb$ couplings, with best bounds found for $\gamma_+ e^-_L \to e^- t
\bar b$ and $e^+_R e^-_R \to e^- \nu_e t \bar b$.
