What character models guide narrative best? Do we want role models or blank canvasses?

For all my talk of emergent narrative and it's wondrous effects on games, I haven't really covered the core promoter of it:- The player character. Even in board games they are the most important piece of the puzzle as they are what the player uses to identify themselves in the game world, to find their place if you will.

In my humblest of opinions there are two main types of character for the player to control. The role model and the blank slate.

The Role Model 

This is the character that has his or her own opinion and likes to let it be known. This type of character might be able to affect the player, to push his/her decisions by either their own force of personality or by suggesting their opinion to the player at a key decision making moment of the game. They still allow the player freedom to decide their own way through a story, but exist to help push the story along the 'right' path.

The Blank Slate

This character is the epitome of a player 'doll'. In extreme cases nothing about them is defined before the player gets their hands on them, in moderate cases they are merely vestiges through which the player becomes a living resident of the game world. Blank slates give the player total unhinged freedom to take the game's story along the path they desire (obviously within the scope that the designer has set out for them).

Both types of character have their benefits - the role model provides for an easier tied together story as there is one more (major) acting in every scene, whilst blank slates give the player a larger amount of perceived freedom, and in turn give them a greater sense of personal investment. The question posed however is do we as gamers want one over the other? I don't feel like that's a question that I have the authority to answer. But if I were to impose my opinion on the subject well... I like blank slates, I like to believe I'm a living, breathing, walking, talking person in the fantastic worlds set before me.

What do you like?