Concentrate one one story, or flit between several?

I decided to do Camp NaNoWriMo this month and set off with my sci-fi YA story quite happily. Two days later I found I wanted to write something different - a short story from a prompt 'better than divorce'. A few days after that, work got in the way and I found myself writing a feature about a trip to Cardiff. Then I got a great idea for another mystery/romance story that I had to start getting down on paper.

The upshot is that at the end of this month I seem to have half a dozen partly formed stories and nothing finished. It's quite frustrating.

Question is, should I just plug on with one until I finish it and then move onto the next, or keep flitting on the expectation that at some point I will finish at least one of the stories? If I had specific inspiration for one story I would work on it now, but I don't, and I've learned not to rely on inspiration to keep me writing!