The problem you're going to run into here is "What constitutes a duel?"
Is it a typical lane fight? Both sides try to harass a tiny bit, the person who lands theirs but avoids / mitigates the others then engages and tries to force a nasty trade on their enemy / all in?
Is it safely harassing the other person to death without committing to a fight / keeping their distance?
is it a scramble between large creep waves, both sides jockying not just to fight their enemy laner but hopefully to mow down the enemy wave at the same time in order to earn a damage edge via their own creeps?
Is it meeting in the jungle at a camp and trying to juggle its aggro onto one another to win?
Traditionally speaking, a duel is what Trundle or Jax want. Where they walk upto you, right click, and proceed to pound your face into oblivion whilst (ideally) standing in one spot while you do the same. In that regard.. Trundle and Jax are basically the best, with a couple of other contenders such as Aatrox, Yi, or Riven depending on what stage of the game it is.
When you start bringing in lots of other factors such as level disparity, creep waves, where the fight is, ect ect it becomes a much more malleable concept. In a we-stand-here-toe-to-toe-and-fight engagement, Jax beats the ever-loving snot out of Darius at most stages of the game. However in an actual creep wave in the lane phase, Darius is quite capable of handling Jax by harassing with Q every time he tries to CS and using his E to briefly dis-engage all ins and turn them around once the counter-attack has expired.