Aperture is the unit of measurement that defines the size of the opening in the lens that can be adjusted to control the amount of light which is let into the digital sensor. The size of the aperture is measured in F-stop.
The first image is my best image because the aperture is low which makes the object (shell) stand out and look more in focus. This keeps the audience looking at the object in focus. In my opinion, I dislike the second image because it is over-exposed/bleached out and the aperture is not correct as the object in focus is quite blurry. The composition of the photo is not correct because it is too low down.