Superconducting YBCO c-axis oriented thin films have been grown by MOMBE (metalorganic molecular-beam-epitaxy). Growth of the films on different substrates  (Y,Nd)AlO3,  SrTiO3 and  MgO has been investigated by in situ monitoring the reflection high energy electron diffraction (RHEED). The paper discusses our results suggesting significant differences in films growth on the three presented substrates. The highest quality (high uniformity, epitaxy and low roughness) has been attained for the films prepared on SrTiO3. All films, regardless substrates, have shown values between 81 and 84 K for zero resistance critical temperature Tc0.