Of these two options I really like open - but I couldn't wear it. I am very busty and that would just not be classy at my own wedding! I like sweetheart the best.
The picture of the open neckline is toooo open for me. I need to wear a bra so this wouldn't work. I have a rounded neckline a little deeper cut than the picture of the "closed" neckline. I always thought "closed" meant right up to the neck.