I like having a few WIPs, (which are completely different from UFOs). They are usually at different stages, or they are different techniques. I cannot imagine just working on one project at a time, start to finish.
My WIPs always include several projects to work on by machine--one that is being quilted, one being pieced and a Leader/Ender project. My L/E is usually stitching crumbs or scrappy 4Ps with no particular plan in mind. Now that I have an embroidery machine, I might add another project I can set to work when I am doing something else in the same room.There might also be a BOM or mystery quilt in the works, but other than the 365 challenge, I am trying to avoid those until the UFOs are under control.
I also have a "quiet -time" project I can do by hand (quilting or applique) if my hand is cooperating and I want to just sit quietly in front of the TV.
In addition, I have "on the go" projects in a bag that I can just pick up and leave the house with. I keep my handstitching supplies, patterns and fabrics for a few blocks and in the bag. Right now, it is a Dear Jane Quilt, which is my long term project that I am hand piecing and hand quilting. It's great to have something to keep me busy while I sit in the waiting room when I take my mother to the doctor.
I take a no-sew day every week, where I clean up my sewing area, cut scraps and decide what my WIPs for the week will be. Sometimes they stay the same, but if I am at roadblock on a particular project, it gives me "permission" to set it aside in favor of something else. Sometimes my WIPs overlap--my stack of crumb blocks was getting tall, so this week my crumbs are my L/E and my piecing block. Last week, my go-bag project was also my "quiet-time" project.
I guess it is a lot of projects to work on at one time, but having a plan is helping me make progress on my UFOs and keeping me from starting new projects.