Mysterious Stranger |
They are similar but the biggest difference I see the archeologist is actually better at trickery and deceit that the investigator. The bard can affect others with his spells, while an investigator only affects himself, even with spells that normally affect others like haste. The bard has access to illusion and enchantment spells that the investigator simply does not have.
The bard also gets 0 level spells some of which are very useful. Detect magic and mage hand are incredibly useful for a rogue type character.