The growth of certain SiC polytypes by molecular beam epitaxy (MBE) under near equilibrium conditions, such as low rates and high temperatures, was analyzed within the framework of classical nucleation theory. It has been demonstrated that the formation of certain polytypes in the nucleation stage is due to an interplay between their differences in the surface and formation energy as well as the growth conditions. Based on these considerations, it was obtained that the formation of a polytype in the nucleation stage is established by a set of growth parameters: substrate temperature, Si/C-ratio and C-flux. The obtained results agree very well with experimental findings based on sublimation bulk-growth experiments as well as with results obtained recently by MBE.