both had new styles and celebrated freedom and movement in women's clothes
had different styles between them, Vionnet focusing more on cut, Chanel more on the style
used drape, took inspiration from Japanese designers used origami
brought about the bias cut dress, was previously just used for collars, this had a better fit
tended to let the fabric control the shape and effect of the garment
rarely used motifs/embroidery, if she did - sparingly, let the shape speak for itself
I particularly like the way Vionnet drapes the fabric, the final garment always enhances the women's figure. The finished garment, is soft, flowing and elegant.
During the 20's Chanel was the first designer to use jersey in women's clothes, it had previously been used for men's underwear. This created a more relaxed style that contrasted to the stiff corsets they were used to, which were now, by many, seen as impractical and uncomfortable. Chanel sported a striking bob and tan so as well as a designer, was seen as a style icon. In 1925, she created the cardigan jacket and in 1926 the little black dress, both of which were very popular at the time, and still to this day remain key garments in current Chanel collections. The little black dress was new because the colour had always been associated with mourning, Chanel flipped this, designing a dress for glamorous evening occasions.
Chanel also produced beaded dresses, designed for the flappers of the time
research taken from http://www.thebiographychannel.co.uk/biographies/coco-chanel.html
images from http://www.elle.com/fashion/spotlight/coco-chanel-portrait-1920#slide-1 and google images