Both dresses are appealing in their own way, but the kicker for me was that you mentioned that you might end up busting out of the first dress. There's a time and a place for flashing excessive cleavage, but I suspect your good friend's wedding isn't that place.
I like both, but I'm so turned off by the way the model's, um, global endowments, look in the blue dress that I say pick the striped one and wear it with gold shoes!