I actually prefer the appearance of no helmet most of the time, because I like to see my character's face when I enter the menu screens, though in Olaf's case the hood clearly matches his secretive nature. In fact, in his case I go so far as to keep him turned to the left so that is face is almost completely hidden.
I'm preparing to complete my trinity and start my paladin Maia (she will follow a custom class I designed, called Silver Knight), and it got me thinking about what sort of things she'll do and what sort of armor she'll wear. I'm also giving thought to appearance, and I realized most of the heavy armor helmets almost or completely cover the head and face (which makes sense). Which makes me think she might not wear a helmet at all, stats be damned! Because in the case of Maia the appearance I am designing plays a large part in how I will RP her.
Does your character wear a helmet? Just wondering.