This work investigates a comparative study between Ni-Zr and Co-Zr substituted Sr-hexaferrites (HFs). SrCoxZrxFe12-2xO19 HFs (denoted as SrCoZr HFs) and SrCoxZrxFe12-2xO19 HFs (denoted as SrNiZr HFs) were fabricated via sonochemical approach. X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR) and high-resolution transmission electron microscopy (HR-TEM) analyses revealed the creation of M-type hexaferrites. The hexagonal-platelet shape is observed by scanning electron microscopy (SEM). The total energy calculations were performed via density functional theory (DFT) on model systems representing the synthesized structures to determine their structural and magnetic properties. The magnetic properties of various synthesized SrCoZr and SrNiZr HFs were evaluated at (RT; T = 300 K) and (T = 10 K). The M-s (saturation magnetization), M-r (remanence), H-e (coercivity), SQR = M-r /M-s (squareness ratio) and n(B) (magnetic moment) were determined. M-H hysteresis loops of various products revealed their hard ferrimagnetic (FM) nature at RT and 10 K. Lower Co-Zr co-substitution contents (x <= 0.04) were discerned to reinforce the magnetic traits of the resultant Sr hexaferrite significantly when compared to the pristine (x = 0.0) one. However, the Ni-Zr co-substitution in Sr HFs provoke a reduction of magnetic parameters.