I love the look of either dress over jeans- and I don't think you need to be a teenager to rock that look at all ( I do it all the time, and let's just say I remember MTV's first video!)
My only suggestion would be to not wear bootleg jeans underneath; I think skinny or straight is a better proportion...
And as far as what photographs better, maybe you can bring both dresses and take pics in both? I think it really depends on what kind of background you'll be photographed...and I"m assuming it's a color pic, not black and white?
Don't worry too much, it's obvious you have great style and will look great no matter what you end up picking! Good luck!