The Creative Process: The Fork In The Road

As I get closer to narrowing down my choices for my next attempt at a screenplay, I've come across a quandry.  While there are still a few other contenders, I've basically narrow my choices down to two.

The first is something that came into my head in the past couple months and spent a lot of time there.  I've got a pretty good idea of what most of the major characters are like, I know the basic details of the plot, and I can play some parts of it on the "3-D IMAX of my mind."  This one would be considered "the safe choice."  I think it has quite a bit of potential and really could be a large step forward for me as a writer because it's very different than my first screenplay.

The second is something that I just had a glint of an idea for very recently.  I've spent practically no time working on it save for the past few days when it's been dominating my thoughts.  At this point, I've got a basic idea of the two characters, I have a very broad, overreaching idea of the plot without much in terms of detail, and while I can play out a few scenes in my mind, there are a lot of very large holes in the plot that I'm not sure what fills in those gaps.  This one is a genre that I have always loved and always wanted to do something in - but this one's risky.  I love the basic premise of it but I'm afraid I won't be able to flesh it out in time.  I can see a ton of potential in it and it would really challenge me as a writer because it won't be easy at all to pull it off.

So, there lies the fork in the road...

With a deadline approached, do I walk the road more traveled and knock out the one that's been dancing around my brain for a couple months?  Or do I take that more deserted path that has a lot of roadblocks on it but a more satisfying "end of the trail" moment?

Suggestions are welcome!