I voted Rogue - because they have the biggest imbalance between their expected role (front line scout) and their survivability.
Monks are very good at not dying; they may not add much to a party but IME are often 'last man standing'.
Bards are weak, but their role is much less dangerous than the Rogue's.
I run a mostly-human & humanoid game, certainly most foes are sneak-attackable. The party Rogue is a handy Spot/Search/Listen machine, but very very weak in combat; certainly overshadowed by the Fighters, Cleric, Druid, Wizard et al. It's ok for a non-warrior class to be overshadowed by the melee classes (Fighter Paladin Barbarian), but I'd think they ought to be comparable to the non-meleer spellcasters like Clerics.
Monks are very good at not dying; they may not add much to a party but IME are often 'last man standing'.
Bards are weak, but their role is much less dangerous than the Rogue's.
I run a mostly-human & humanoid game, certainly most foes are sneak-attackable. The party Rogue is a handy Spot/Search/Listen machine, but very very weak in combat; certainly overshadowed by the Fighters, Cleric, Druid, Wizard et al. It's ok for a non-warrior class to be overshadowed by the melee classes (Fighter Paladin Barbarian), but I'd think they ought to be comparable to the non-meleer spellcasters like Clerics.