Sanchez has been here for 6 months, been shite for about 60% of it and barely speaks English. No thanks.
Out of the senior (age-wise) members of the squad, only Young would be a good choice. That depends on if he's starting though (hope not). Not that I pay much attention to it, but Matic doesn't seem to be much of a talker on the pitch. Mostly just gets on with it. Valencia, while being a model professional and spending a large amount of his career here, doesn't speak English, doesn't really lead his team and seems to have declined. He'll probably still get it, even if he doesn't play all the time, just because he was the default captain this year.
Another player that could be considered is Pogba. While inconsistent, Pogba has charisma, is vocal on the pitch, has a good rapport with his teammates, has long-standing links with the club and importantly has quality. It's not likely next season, but I'd imagine he'll be one of the main candidates long-term. I remember him wearing it in successive games before his injury. Seemed like a good fit back then. Lukaku definitely isn't lacking in passion, but other than giving out the usual thumbs up in response to an attempted pass, he doesn't communicate much. De Gea may be a fantastic player, but I don't see what he brings to the table in terms of leadership. Him being a good player won't mean much when, a lot of the time, he won't even be in the same half as the ball or ref. Herrera has everything other than starting quality, unfortunately.