I love Marchessa dresses. But, in here, I will go for BCBG, so sexy and goddess like, Grecian. I LOVE IT. Marchessa one is more feminine very elegant. I'm more into sexy style. Depends on your personality.
I think the BCBG is great - nice shape and looks comfortable as well. With the right accessories, it could be dressed up or down a little. Marchesa is nice, but perhaps a little too frilly.
I think I'd need to see your face to see if blue or white suits you better. The first one is a definite "no" for me because it is noticeably big. Just doesn't fit.