Mezzo's pluck the strings of my heart! Right next to that, (bass-)baritones (I might be slightly biased on this one seen as I am a baritone). Christa Ludwig and Fischer-Dieskau made Lohengrin's act II one of the best musical experiences ever for me (for those interested in this, check out the Kempe recording with Wiener Philharmoniker, Jess Thomas and Elisabeth Grümmer in the major roles. Completaly worth it for Ludwig and FD alone!).