I suggest this thread for some great ideas of what to wear:
http://www.greekchat.com/gcforums/sh...d.php?t=115173
Your second and third dresses aren't my personal style, but they could be okay if they won't be too short, too tight, or show too much cleavage on you. You want to look classy and pretty, and not trashy in the least. You also want people to remember how wonderful YOU are, not whether your dress was too short or too loud or too cheap-looking or too ... whatever.
The first dress, though, I'd scratch for sure. It's a terry cloth beach cover-up robe. It's an expensive one from a well-known label, but ... it's a terry cloth beach cover-up robe.