probably Jefferson tbh; if we're talking slavery he did far more damage to its viability as an institution than Robespierre (given the Girondins had abolished it before him e.g. Sonthanax in Haiti, not to mention the efforts of the rebellious slaves themselves; and after he fell from power slavery would be reinstated and not be banned till the Second Republic.
That's something a lot of people don't consider about Jefferson. Despite being a hypocrite and personally owning slaves his ideas directly lead to the abolition of slavery. So his impact goes far beyond just his own personal life in that area and is net positive. Same type deal with Gandhi.