Systematic studies on the ABa2Cu3-xMxO7(R=Sm, Dy; M=Fe, Ni, Zn) system were carried out in order to determine the effect of the rare-earth ionic size and magnetic moment on the Tc suppression rate. The phases were characterized by powder x-ray diffraction (XRD), resistivity, and ac susceptibility measurements. XRD studies indicate a higher solubility limit of M ions in the SmBa2Cu3-xMxO7 [Sm-123(M)] system as compared to the DyBa2Cu3-xMxO7 [Dy-123(M)] system. Resistivity and ac susceptibility studies indicate that the Tc suppression rate for a given M ion depends on the ionic radius of the rare earth (R) and is higher for larger rare earths. The trend in Tc suppression as a function of concentration (x) shows deviation from AbrikosovGor'kov behavior. A metal-insulator transition is observed at higher dopant concentrations, and the semiconducting phases are found to obey the Mott's variable range hopping mechanism of conduction. The parameters related to hopping conduction; viz., the characteristic temperature (T0), localization length (a), hopping range (R), and hop energy (W) have been calculated, and a comparative study of the variation of these parameters in the two systems has been made.