The Stakes Character

Who exactly will be the 'Stakes Character'? That's the question for me at the moment. I want to be able to get this really clear, as I don't want to head down a path only to have to return to square one because I've made the wrong decision. 

In my screen story there are two possible characters that could be the Stakes Character, one is the hero's best friend (female) and the other is the hero's female object of desire. I'm leaning towards the 'object of desire' and will keep best friend as 'mentor' in a way... I know it seems pretty cut and dry, but I just want to fully understand the function of the Stakes Character in the story overall.

To structure my story, I'm currently using 'Contour for Windows'. It's definition of 'Stakes Character' is as follows:

The stakes character is the human face that represents all of the people that the bad guys are victimizing. It's usually someone personal to the hero, or the hero feels very deeply about. In this plot point, we see what's wrong with the hero's life via the life of the stakes character. Most heroes are usually flawed or wanting in some way at the start of a film. The stakes character usually has the qualities that the hero needs to complete his arc.

My questioning of the which character should be the stakes character stems from this statement. The hero cares about both of these characters, and the 'object of desire' is victimised, but she doesn't necessarily have the qualities that the hero needs to complete his arc, as she is down-trodden by her husband and lives a pretty miserable existence with a dark secret... BUT...

... but that may be it. The hero does not know this fact, the fact that she is miserable in an unhappy, emotionally controlling marriage. Our hero only sees from outside of her life and wants that with her. The hero is jealous of the life she leads without him, and wants her for this fact. It won't become apparent to the hero until later in the story (second act) of the life she leads. Ok, I think I've got it.

The example in Contour is a 'nutshell' example, and stories can be infinitely more layed or complex to explore this concept. Here's a great link that goes into considerable detail about the stakes character check it out . Basically, the writer states that the stakes character is the character the hero has to rescue.