  We calculate the decay constants of light and heavy-light pseudoscalar and
vector mesons with improved soft-wall holographic wavefuntions, which take into
account the effects of both quark masses and dynamical spins. We find that the
predicted decay constants, especially for the ratio $f_V/f_P$, based on
light-front holographic QCD, can be significantly improved, once the dynamical
spin effects are taken into account by introducing the helicity-dependent
wavefunctions. We also perform detailed $\chi^2$ analyses for the holographic
parameters ({\it i.e.} the mass-scale parameter $\kappa$ and the quark masses),
by confronting our predictions with the data for the charged-meson decay
constants and the meson spectra. The fitted values for these parameters are
generally in agreement with those obtained by fitting to the Regge
trajectories. At the same time, most of our results for the decay constants and
their ratios agree with the data as well as the predictions based on lattice
QCD and QCD sum rule approaches, with only a few exceptions observed.
