What to write?

For the last month, I was sure I knew what project I wanted to work on during January. I have done lots of pre-writing (plotting, characters sheets, all the stuff I never, ever do when I write a book!) on an idea since the summer because it's a little different from the regular Harlequin Romances (HR) I write, and I've always intended to write the entire manuscript before submitting it. That's called writing on spec for all you non-writers out there. I haven't done that since my very first sale to Harlequin Yours Truly.

Of course, now an idea for an HR is keeping me awake at night. I'd asked my editor about making one of the secondary characters from my recent November release a hero of his own book, and last week she said to develop the idea for her. Granted an idea is far from approval to write a book, but at least this one has a great chance of publication since I owe them another book in the fall of 2009. The other idea is something I really want to write, but I can't say anyone will buy that manuscript.

Still I really don't have much on the new idea. If I write this one for JaNoWriMo, I would be flying into the mist so to speak with a hero, his dog and a setting. Nothing else. I wonder if I'd be writing it too soon since I usually let ideas percolate in my head while I write another book.

So today I have to decide which one will be my JaNoWriMo project. Any suggestions on making that decision?