That's tough... At first I thought Jaden, but that actually seems a very tiny bit more feminine to me b/c of the name Jade in there. Plus, if you want the option of the nn Jay at any point, Jayden may work better. I think either is fine, but I'd choose Jayden.
I think Jaden looks more masculine. Also, if you want to use the nn Jay (a pp mentioned it) I know plenty of boys named Jason that go by Jay so the lack of the y won't be a problem.
Re: Which way to spell?
Jaden
the Y makes it look feminine to me.
I agree with this.
Ditto.