  We evaluate the theoretical uncertainties in next-to-leading order plus
parton shower predictions for top quark pair production and decay in hadronic
collisions. Our work is carried out using the Herwig 7 event generator and
presents an in-depth study of variations in matching schemes with two
systematically different shower algorithms, the traditional angular-ordered and
alternative dipole shower. We also present all of the required extensions of
the Herwig dipole shower algorithm to properly take into account quark mass
effects, as well as its ability to perform top quark decays. The predictions
are compared at parton level as well as to LHC data, including in the boosted
regime. We find that the regions where predictions with a
non-top-quark-specific tune differ drastically from data are plagued by large
uncertainties which are consistent between our two shower and matching
algorithms.
