Behavior of C60 and C70 fullerenes adsorbed onto Si(111)3×3-Ag is compared on the basis of STM observations. Such characteristics as sticking coefficient, migration rate, attachment/detachment rate from the molecular islands are considered. Room-temperature sticking coefficient for C70 is slightly greater than that for C60. Due to their non-spherical shape, C70 are less mobile than spherical C60. For both types of fullerenes, mobility of molecules on the fullerene layer is significantly retarded as compared to that on bare Si(111)3×3-Ag surface. Self-assembly of C60 obeys layer-by-layer growth mode, while C70 follows multi-layer mode, a sign of a greater Ehrlich-Schwoebel barrier. Alternating deposition of C60 and C70 paves the way to fabricate planar C60/C70 heterostructures with the most promising results being obtained with nanostructured islands grown on C60 monomolecular layer.