If you ran for President...

[Leinad]

A combination of these two factors:

Last, because it's shorter and catchier.

I remembered another factor: my name is getting more popular, and by the time I'm old enough to run a serious presidential campaign, my name might have increased in popularity to the point where it would be like saying "Vote Jim 2016!" So in that case, I'd probably rather use my last name.

Although I'd use my first name a good bit as well, as a way to appear more down-to-earth.