Virb EDIT Export resolution

Hi,

I am looking to find the right settings to export videos that I have made with VIRB edit. What's the right setting for resolution, (FPS if you can change it) and quality to make the most of the the camera recording at HD 1080 with 25 or 30fps?
I seem to end up with either larger or smaller file sizes than the original clips, whih I understand to mean that I eitehr lose quality or needlessly enlarge the file? Many thanks