I voted no for all of them. The reason? Unscrupulous players will find ways round this all to grief and gank unsuspecting players. I saw it in WoW and countless other games that allowed open world PvP and human nature dictates that in every walk of life there are the trolls and [censored] who get a kick out of someone else's discomfort. Let's not, eh? We play this game for fun and if a player can only get their kicks by watching someone else suffer then I think they need to see a shrink...
And no to duels. I've lost count of the number of times in other games I have been challenged by some bouncing spastic ten levels above me who only wants an easy kill. I would only accept a duelling system if there was an auto-decline option built into the settings interface.