The dynamics of formation of the macroscopically occupied polariton mode at the bottom of the polariton band E LP(k = 0) and its spin polarization under the quasiresonant pulse excitation of excitons (E = E X ) with large values of quasi-momentum have been studied in planar GaAs microcavities. It has been found that the growth in the depth E X − E LP(k = 0) of the polariton band leads to the change in the formation mechanism for the k = 0 condensate state from the direct parametric decay of the photoexcited mode (due to the polariton-polariton interaction) to the dynamic condensation of polaritons, which results from the multiple scattering of polaritons by both phonons and polaritons. At the same time, in microcavities with E X − E LP(k = 0) > 3.5 meV, the direct decay of the photoexcited mode does not disappear, becoming an efficient mechanism for the filling of the states located at the k-space ring, corresponding to the energies E LP(k) ≈ E X − 2.6 meV.