Someone who rocks the boat, someone charming and interesting like Han was.
Someone American.
I always thought that the best accent for Han would be some kind of Irish accent, but this opinion of mine is based on what I’ve read in EU books, especially about Corellia and Corellians. The Corellians have always been portrayed as independent, adventurous and proud people, eternal explorers, who portray all the classic stereotypes of romantic ‘good’ pirates/smugglers, who like drinking, gambling, fighting, like profit but still have the sense of honour, that’s why they’re always on the side of good. That corresponds very highly with some of my personal stereotypes about the Irish people, and I find this image very appealing. (Hope none Irish is offended and sorry for mistakes – English is not my primary language 😃) That’s why I think that some kind of Irish accent would be a killer feature for Han.
P.S. And one more thing – in EU all Corellians love green 😉