We present a systematic study of the influence of the processing conditions on the charge-carrier mobility in hole-only diodes and field-effect transistors (FETs) based on alkoxy-substituted poly(p-phenylene vinylene) (PPV). It is demonstrated that by chemical modification from asymmetrically to fully symmetrically substituted PPVs the mobility in both types of devices can be significantly improved. Furthermore, for symmetrical PPVs the mobility is strongly dependent on processing conditions, such as choice of solvents and annealing conditions. The increase in mobility is accompanied by a strong enhancement of the anisotropy in the charge transport. Ultimately, mobility of up to 10-2 cm2/Vs in FETs and 10-5 cm2/Vs in hole-only diodes have been achieved.