Shorsand

I think the persona name should be the name most associated with that person. Usually, a surname is quite well associated with people. I tend to remove them only when adding a title, as most people with titles don't go by their surname. You don't say Charles Windsor, you say Charles, Prince of Wales.

Using my old character as an example, I went by Nicolas Barclay for the vast amount of my youth. When I became a Holy Knight, I changed my persona name to Holy Sir Nicolas (much to the consternation of the other Barclays).

I've ended up not putting my surname for simplicity's sake and not using too many characters. 

Once in a blue moon you find someone who metagames you cause they see your surname in your player tag as well so it's also best not to have it sometimes.