What Comes First

I constantly marvel at how authors who have day jobs, or children, manage to get any writing done. I've retired from the 9 to 5 scene, and now that Sis has moved out, I only have my dog depending on me, so it should be a piece of cake for me to get my work done, right?

Wrong!
I'm currently juggling three jobs at the same time–my current WIP, edits for the contemporary, and my ghostwriting job. So which do I tackle first? The one that's bothering me most? The one that's the most pleasant? The one that will pay me? Work on all three simultaneously? 
My method used to be quite simple. When I lay in bed at night, which project is it that I think about? If the project is keeping me from getting to sleep, that's the one that needs taken care of first. But, of course, that's not the case with my current situation. I'm constantly thinking about each of the projects, but from different perspectives. So the best approach for me right now is to work on them all at the same time. Since they are totally different in terms of era, genre and tone, I won't be mixing story lines, so I should be okay there. But I won't get a good night's sleep until at least one of these is off my plate and onto someone else's. 

So tell me–what's your method of dealing with multiple projects?