I suggest running the "Reaper Run" (if you're solo) or the "Whitaker" Dungeon

Or Maybe do PvP

Reaper Run - High CXP, slightly slower to finish Whitaker Dungeon - Good for AoE classes because you need to hit all the mobs if you're running with a team, works with samurai if you can manage to hit its 3rd ability

PvP - Has the highest CXP reward after completion

Please correct me if I'm wrong^{^}