In your opinion, which hero has the most charisma in the campaign?

Firstly. And secondly, no matter how cool he is (if he were cool, although he simply has better conditions from the start, like the Warlock), his charisma only extends to demons.

Tieru killed the Warlock's servant.

There was a druid meditating on the island, and then a demoness arrives with an entire army. Just because Tieru is a great druid doesn't make him a superman. ------

Only the Warlock figured out how to use two unremarkable women to turn Ashan into ruins.

Biara and Jezebeth? Well, Biara started acting on her own towards the end, and Jezebeth is quite the character: she was hanging out with Aidan even before the events of H5.