Depends on the kind of PvP you’d like to do. The worst one PvP wise is WP Sura, however, since its a hard server, with a very limited access to changers, any class could perform to some degree if You got great EQ. If You compare classes with equal eq, then certainly Light shaman, Sura BM And Mental would be ahead.
Now from my perspective and experience from Dojang and open pvp:
For Dojang lv 39 bracket: Shamans are absolutely broken
For Dojang lv 59 bracket: Shamans still shine, but BM becomes more valid, so does the mental and ninjas
Won’t comment on the higher bracket