We present spin wave dispersions in MnO, NiO, and $alpha$-MnAs based on the quasiparticle self-consistent $GW$ method (qsgw), which determines an optimum quasiparticle picture. For MnO and NiO, qsgw results are in rather good agreement with experiments, in contrast to the LDA and LDA+U description. For $alpha$-MnAs, we find a collinear ferromagnetic ground state in qsgw, while this phase is unstable in the LDA.