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A comparative study of the electron transport properties of MgB2 bulk samples was performed aimed at addressing the role of annealing as well as of SiC and Zn doping on sample anisotropy and band conduction parameters. Samples were produced by Reactive Mg Liquid Infiltration (RLI) technique in boron powder preforms. Both irreversibility (B irr) and upper critical fields (B c2) are enhanced by doping procedure. In all samples the B c2 anisotropy factor (gamma), evaluated by analyzing the B irr and B c2 temperature dependence in the framework of the current percolation model proposed by Eisterer et al. [Phys. Rev. Lett. 90, 247002 (2003)], decreases at increasing temperature, and it is reduced by SiC and Zn doping-induced defects. Accordingly, in both annealed and doped samples the pi -band diffusivity, obtained by fitting the B c2 dependence on temperature within the two-band model formulated by Gurevich [Phys. Rev. B 67, 184515 (2003)], is higher than the sigma-band one. A decrease of the more anisotropic sigma-band diffusivity was also found in the doped samples.