I decide what screenshots get selected. A lot of the features you mentioned go into it: creativity and quality for sure. Talking about each of these though:
-Creativity: new approaches to screenshots are always good moves. Some examples of great creativity:
Is it a coincidence that they're all Alitalia? Maybe not, for Italians have great style...
What's especially uncreative: a cockpit shot that has nothing interesting outside
-Quality: please take a look at my suggestions for creating good screenshots here
. If a screenshot is breaking one of those, it had better have some other redeeming features. For instancel, nothing looks worse than an aircraft with a tiny bit (like a winglet or part of the tail) cropped out.
Some other factors come into play as well: as a general rule, I try not to select more than three of the twelve screenshots to come from a single person. Also, if there are two (or more) really good screenshots that are very similar from the same person that are worth adding, I generally only add what I think is the better one to avoid vote-splitting, which would hurt the author.
I only vote in contests to break ties.