Which one of these dresses should I wear to my sister's wedding?

The wedding is taking place next year, in the springtime ( mid April, I believe). It will be taking place outside, and we know it will be nice weather. I am going to be her maid of honor, and I am blonde (natural), about 5'4" and 18 yrs old.

Which dress should I wear? http://www.polyvore.com/cgi/set?id=49630989

Let me know your opinion!