Personally, I never use fixed aspect ratios for serious images unless I have to--for example, if a display requires it. I allow the image to determine what should be cropped or left, and that leads to idiosyncratic aspect ratios. For example, this one has an aspect ratio of 1.43:1, determined by creating a pleasing amount of negative space around the plants:
This one is 1.78:1, to avoid distracting, irrelevant detail:
The cost of this, which was driven home to me recently when we moved to a smaller home, is that one collects a lot of expensive frames that later go unused. I deal with that sometimes by finding a frame that is approximately right and cutting a mat that has different side and top dimensions.