  We compare the physics potential of planned superbeams with the one of
neutrino factories. Therefore, the experimental setups as well as the most
relevant uncertainties and errors are considered on the same footing as much as
possible. We use an improved analysis including the full parameter
correlations, as well as statistical, systematical, and degeneracy errors.
Especially, degeneracies have so far not been taken into account in a numerical
analysis. We furthermore include external input, such as improved knowledge of
the solar oscillation parameters from the KamLAND experiment. This allows us to
determine the limiting uncertainties in all cases. For a specific comparison,
we choose two representatives of each class: For the superbeam, we take the
first conceivable setup, namely the JHF to SuperKamiokande experiment, as well
as, on a longer time scale, the JHF to HyperKamiokande experiment. For the
neutrino factory, we choose an initially conceivable setup and an advanced
machine. We determine the potential to measure the small mixing angle sin^2 2
theta_{13}, the sign of Delta m^2_{31}, and the leptonic CP phase $\deltacp$,
which also implies that we compare the limitations of the different setups. We
find interesting results, such as the complete loss of the sensitivity to the
sign of Delta m^2_{31} due to degeneracies in many cases.
