Topic: I'm going to write a story, but need opinions on which one to choose?

I've been holding this off for a long time, but I plan on writing a (hopefully) book-length original story on FictionPress, but I'm stuck between two ideas and don't want to do both at once. So which of these two do you think I should go with? Now keep in mind that both of these are the very first concepts, so details are gonna be scarce.

#1 Ornithicha: World of Water & Sky

This story takes place in the far future (a few thousand years or so) after the wake of nuclear war, and thanks to misfired missiles the polar ice caps have completely melted from the explosions, leaving most of the world underwater. Now two separate groups of people have come out of the cataclysm, with one building a civilization under the sea akin to a modern Atlantis, and the other a network of floating cities that drift about in the atmosphere.

#2 Untitled (for the time being)

This one is a bit more simple. A shy but curious teenage boy that lives with his super-genius scientist dad in a secret laboratory accidentally walks into a strange chamber when nobody was looking, which turns out to be a DNA fusion machine. At the time his father was attempting to create the ultimate seed by combining the DNA of all vegetation via the fusion machine, and thus possibly solve the problem of world hunger since the result could grow anywhere. And so when the teen stumbles into the contraption (haven't picked a name for him yet btw), the experiment is set in motion and he comes out with the ability to control all plant life to his whim.

There are several ideas I'm throwing around with this one, like an evil scientist who used to work for the boy's father as an antagonist, and a girl who is basically a man-made angel as a result of illegal experiments committed by the bad scientist mentioned earlier who could be the teen boy's love interest. Obviously off the bat this sounds like a cliche superhero story, and while it certainly takes inspiration from that kind of stuff I don't plan to write it quite as such. For example the teen isn't going to run around in a costume fighting crime and such.

So which concept do you guys like better?

Honestly, I'd say go with the one you have more of a solid idea for what you want to do. The second one sounds like you got it more fleshed out in your head, and if I were you, I'd capitalize on that momentum. Plus it sounds like it might be a tad easier and more fun for you to write, which I'm assuming is why you're writing in the first place, right?

Just as an aside, I know I'll be writing 10 or so short stories (like, really short - 10-50 Pages per story is what I'm shooting for) next year, just to give myself some writing practice.

@CanisWolfred Funny thing is, the #1 story was actually the one I came up with first, however a number of factors from #2 came from a Smash Bros. fanfiction I wrote a while back. It was one of those "insert your character (also known as OCs)" things, I'm ashamed to say. But anyway the whole how the teen got his powers came from that, and the angel girl was an actual angel who was Pit's sister (real original I know).

But yeah, I think I'll try my hand with #2. Time for some brainstormin'!