Dynamic is better. Dynamic means more energy, force, and interest:
1. Look at the background
When shooting selfies, take the background into account. Ideal to have interesting shapes, forms and objects in the background.
For example this selfie I shot in this pentagonal mirror:
Note how I simplified the shapes and forms to show you the general visual gist of the composition:
And a side by side:
2. Experiment
Look at the top of the frame, if it kisses the top of the frame:
Note in this example, there is no negative space on top of the frame:
For the second image, there is a bit of negative space on top:
Side by side view:
And small thumbnails: