Its extremely hard. For me i want the captain to be someone who loves the club, gives his all, is big and strong, as well as being a great organisor and man motivator. Now they are all not essential of course, but we have been spoiled as we currently have the exact person i described. It will be a tough decision when it has to be made, but i can only really see it as cahill atm, if you ignore the obvious ones who won't be there for the "future captain" role (I.e. Lampard and Cech). Cech will probably still be there but i think the captain should be an outfield player to better deal with players. I have never really though of david luiz as a possibility, though aslong as he is focused well respected by the rest of the squad and is a leader, then i don't see why not. He is seen as the joker in the team, but without giving him a chance i suppose we will never know. Not who i would choose as of right now, though obviously none of us are in a position where we know him anywhere near as much as the people at chelsea do. Nathaniel Chalobah for future Long term captain but that is still some way off.