We have studied the normal-to-superconducting phase transition in optimally doped YBa2Cu3O7-delta in zero external magnetic field using a variety of different samples and techniques. Using dc transport measurements, we find that the dynamical critical exponent z=1.54 perpendicular to 0.14, and the static critical exponent nu=0.66 perpendicular to 0.10 for both films (when finite-thickness effects are included in the data analysis) and single crystals (where finite-thickness effects are unimportant). We also measured thin films at different microwave frequencies and at different powers, which allowed us to systematically probe different length scales to avoid finite-thickness effects. dc transport measurements were also performed on the films used in the microwave experiments to provide a further consistency check. These microwave and dc measurements yielded a value of z consistent with the other results, z=1.55+/- 0.15. The neglect of finite-thickness, finite-current, and finite-frequency effects may account for the wide ranges of values for nu and z previously reported in the literature.