  The linear and nonlinear pulse propagations in lifetime-broadened three-state
media with spontaneously generated coherence (SGC) are investigated
theoretically. Three generic systems of V-, $\Lambda$-, and $\Xi$-type level
configurations are considered and compared. It is shown that in linear
propagation regime the SGC in the V-type system can result in a significant
change of dispersion and absorption and may be used to completely eliminate the
absorption and largely reduce the group velocity of a probe field. However, the
SGC has no effect on the dispersion and absorption of the $\Lambda$- and
$\Xi$-type systems. In nonlinear propagation regime, the SGC displays different
influences on Kerr nonlinearity for different systems. Specifically, it can
enhance the Kerr nonlinearity of the V-type system whereas weaken the Kerr
nonlinearity of the $\Lambda$-type system. Using the SGC, stable optical
solitons with ultraslow propagating velocity and very low pump power can be
produced in the V-type system by exploiting only one laser field in the system.
