Preferentially oriented thin films of YBa2Cu3O7 (123) and YBa2Cu4O8 (248) with the c-axis perpendicular to the substrate have been prepared by e-gun evaporation from Y, BaF2 and Cu. Critical current and resistance transition measurements have been carried out in magnetic fields parallel to the c-axis. The results will be analysed in terms of a model for thermally activated flux flow combined with two models for flux pinning, one in which the pinning is predominantly caused by twin boundaries and a second in which pinning by dislocations is considered. The resistance broadening in the 248 is well described by the model with dislocation pinning. The Bc2 (T) values obtained from the fits compare well with estimates from the fluxflow resistivity and a kink in the resistance vs field curves. The slope of Bc2 at Tc is 0.37 T/K, a factor four smaller than in the 123.