NaNoWriMo Subject?!

We're about a month out from the beginning of NaNoWriMo. I want to participate this year and (hopefully) actually win this time around - though we'll see. I'm going to try laying some groundwork this year and I have two distinct ideas for the projects I'm going to tackle this time around. I'm torn between them.

The first is sort of this adventure, but set in a fantasy setting that sort of looks like like the 21st century - skyscrapers, smart phones and social media and so on, but it also has all these standard fantasy stuff co-existing with it - elves, dwarves, wizards and the like. The idea is essentially 'what happens if a stereotypical fantasy world actually modernizes' and the plotting sort of addresses it. I have some fun ideas for it - like you go to a zoo to see dragons or gryphons or unicorns. Arthurian castles and ancient wizard's towers and so forth have been converted into historical landmarks and museums.

(This whole notion, incidentally, is loosely inspired from a weird-ass dream I had a while back where Walmart had, of all things, a flippin' Magic department.)

The other idea is sci-fi in flavor and is inspired more from my childhood TV watching (or book reading)- drawing from stuff like Voltron, Power Rangers, Animorphs etc - you know, a group of kids/teenagers get their hands on advanced alien technology and end up drawn into some sort of large-scale, high-stakes war against alien foes.

The premise is basically this: the Earth is invaded by alternate reality humans allied with eldritch creatures from another dimension. A mysterious being gives the protagonists strange futuristic devices that scans animals and creates robotic templates based on those animals that they can then summon to help them fight back. The Earth, quickly conquered, sends them on the run from all that they have known and they find themselves drawn into an epic conflicts, while having character growth, large-scale battles, solving the mysteries of the setting and all that good stuff.

I really like both of these ideas - the sci-fi one has more of a plot going for it but the fantasy already has more of the world-building going on. So help me choose!