Which type of fencing is the most similar to a duel?

Torso. In fencing a target on the weapon used. In foil it's torso without arms or legs, in épée it's entire body and in sabre it's entire body above the waist, except the weapon hand.

Foil with its stip­u­lat­ed rules (such as priority of attack) was the only weapon used at spar­rings. At the same time, in real duels an épée was used, and no such rules were ob­served. Hence, an ex­pe­ri­enced fencer could lose his life to a rel­a­tive­ly weak op­po­nen­t.

Sabre. French grip optimize hitting with the point of the sword (a 'thrust'), which is the only way to score a touch with a foil or épée. In sabre this grip would be un­com­fort­able, as cuts are used.

They're all dif­fer­en­t. Every fencing weapon has a dif­fer­ent shape of blade. Épée is tri­an­gu­lar, foil is quad­ran­gu­lar and sabre is rec­tan­gu­lar.