You can change the aspect ratio when you photograph with a digital camera. Do you like 16:9, 4:3, or did you grow up with 120 film and adore the 1:1 (two and a quarter square) image? When we photographed with film, aspect ratios were decided by the camera and film you chose. When I photographed with a view camera, the “standard” was 4x5, but I really fell in love with the 5x7 format because it was a very elegant perfectly proportioned format.
Do you have a “native” aspect ratio that is set up on your camera? Do you have one that looks best to you, or do you make that decision with each image?
How about landscape versus portrait orientation? Is there one orientation that predominates in your vision? I have noticed that my picture orientation varies by location, with interiors tending toward a vertical orientation and landscapes (naturally) being horizontal. I think that my tendency to photograph with a vertical orientation indoors is a combination of being confined by interior walls and needing to show as much as possible. I think the vertical orientation is the way to show more of the subject. While I don’t have the statistics to back it up, I tend to think of Edward Weston’s photographs being mostly in the vertical orientation. (I think that might be a great MFA project, with a suitably obscure and academic title, of course.)
I am not obsessive enough to chart the balance between horizontal and vertical compositions of my photographs, but I do go through a conscious decision when I sequence images in a folio to maintain a balance between the two orientations.