If I could snap back to my regular size at any point, I would go with the ability to shrink. As a person who likes to learn a lot, it would be great to see everything from the perspective of a bug. I could learn new things about nature as well as see the whole world, as well as our impacts on it, from a different perspective.
Of course, I would hate being an inch tall for the rest of my life, so if the change stuck I would rather be a bit taller so that, when I enter a room, I could make more of an impact.