  The $GW$ approach of many-body perturbation theory (MBPT) has become a common
tool for calculating the electronic structure of materials. However, with
increasing number of published results, discrepancies between the values
obtained by different methods and codes become more and more apparent. For a
test set of small- and wide-gap semiconductors, we demonstrate how to reach the
numerically \emph{best} electronic structure within the framework of the
full-potential linearized augmented planewave (FLAPW) method. We first evaluate
the impact of local orbitals in the Kohn-Sham eigenvalue spectrum of the
underlying starting point. The role of the basis-set quality is then further
analyzed when calculating the $G_0W_0$ quasiparticle energies. Our results,
computed with the \exciting{} code, are compared to those obtained using the
projector-augmented planewave (PAW) formalism, finding overall, good agreement
between both methods. We also provide data produced with a typical FLAPW basis
set as a benchmark for other $G_0W_0$ implementations.
