I am not honestly sure where how I evaluate XP falls, though perhaps story and session are the closest of the categories given. For the curious, instead of just saying I do this or that, I thought some explanation wouldn't hurt. Here is how I explain XP to my players, new and old.
I break things down and these are my top five general categories of experience. I usually evaluate experience for everyone in these categories and provide feedback from my perspective as the GM so they understand how I got the numbers I did for each category (where they apply).
Group: [Essentially, the experience the entire group earns together. This encompasses all conflicts that the group together overcomes or surmounts. This can range from battles to riddles; outmaneuvering a foe, surpassing use of tactics, overcoming an obstacle through combined use of skills, etc.]
Leadership: [This requires a little explanation. Essentially, it is how well you lead within the limitations of your character. This is more than barking orders and getting the party to go where you want them to go. That is only a small portion of the whole. Leadership encompasses how you play your character and whether it inspires the rest of the group or just one other person to role-play more than they did previously. It also holds within it how well you teach the other players to game well; whether by guiding a new player in understanding the rules without taking away from the game or sharing your experience with others.]
Character Development: [Separate from role-playing is how well you develop your character from the first game to the next. Are they always stagnant or do they change with events? Are you taking the time to react and think like your character would? Acting like you were bound or unleashed by their cultural mores? Or to be blunt, is your character a piece of paper dotted with magik items for definition, or a personality that is no more restricted by the paper it is written on than our own?]
Role-playing: [How well do you game? Do you drop deeply into the storyline and reflect on events like your character would? If you are the strong silent type, do you live up to that appellation? If you are the boisterous, but well meaning, do you act that way? Essentially, this is how you played the role you defined at character creation and continue to define in game play. It also encompasses how you make mechanics (adding levels, stat, etc) reflect in game play, the story, and other like things.]
Story: [A measurement of how you interact with the ongoing storyline. Do you change its direction, nurture it along, or build it into something altogether different? This is tightly related to role-playing and character development.]
Every since I have started doing this it has made character development and role playing explode. The feedback makes the players as a whole feel better on how some players can progress faster than others.