So here's where I stand picking the concept to go with. I'm purposefully being vague the particulars in the interest of concentrating on the writing bits.

#1 is an idea I've been kicking around for a while. It's a genre I don't have much practice in (romance), which is both a drawback and a charm. One of the key charms is that the concept lends itself to an 'episodic' structure, which in my experience lends to a longer story for me (if I have a beginning-middle-end, I tend to start rushing to the end). The key drawback is that I can't nail down a struggle, some reason to get the plot moving beyond its root concept. Otherwise it's just a TV drama series of the variety I can't stand, with the environment & characters being static.

#2 is more my traditional territory - "It's not the world as you know it anymore." The inspiration here is largely how disappointed I was with the movies Chronicle, Push, and Jumper. I feel one of the mistakes made in those movies was making the central character too powerful and narrow, so Billy is going to have much lower levels of power but more of them (right now I'm talking about 32lbs of TK, 100 yard teleportation, that sort of level). The big weakness here is that this too normal for me: I don't know if I can keep interested in writing that for a month. I can very easily see this getting to 30k in 10 days and then not getting finished.

#3 is a world I've been kicking around for about three years now. It might be roughly described as being a Naruto-esque world, minus the eye-hax and tailed beasts. This one has the huge advantage that I've already got a lot of the world-building done, and I can do 10k-20k on that alone. The problem is that I've never developed a plot or story for this world.

I am toying with the notion of mixing #2 and #3, with the main character being a new concept for the world -- different enough he'd still be finding everything out for himself, but having the built-in struggle against the status quo.