I think it's going to be heavily dependent on the circumstances. Sometimes you find a gorgeous composition in terms of the overall scene and wait for the subject to enter it. Other times you come across an extremely interesting subject and do your best to adjust composition as best you can in order to capture the image.

This image was me finding the composition and then waiting for about fifteen minutes for the next carriage to pass while this one involved me dropping everything and taking a photo before he moved.

Planned photos are typically much better composed and are technically better while photos taken spur of the moment can have a certain je ne sais quoi that can't be replicated with any amount of planning. The downside is that it's just a matter of luck and not the type you can force.