My favorite part is the design and planning and collecting/playing with fabrics. But I also enjoy the actual sewing part. I am lucky enough to have a designated space and am able to sew each day. And I'm at my happiest with at least a bit of sewing.
Do you have Electric Quilt or graph paper to doodle on? I can get a lot of my fun design play on digitally or on paper without committing to fabric. And yeah, colored pencils, markers or crayons are good on paper. But with EQ you can just click and change like magic.
There is a point in each project where I just want to wrap it up and move to the next one. When people ask me what is my favorite project, I reply "the next one!"
My least favorite part is the clean up, but I've really worked on my skills and that I enjoy having a nice clean space to work in, so the putting away of one project is an important step in both my happiness and the next project.
edit:
@Lena1952 I've started doing quite a bit of weird stuff on paper towels, like practicing freehand quilting motions. They hold up surprisingly well.