Melanie - Optic has peroxide in it so if you must have a toothpaste treatment try that one. If they are badly stained I would suggest a professional whitening tray you will have better results. Whitening toothpastes are not that great.
Abbey - I haven't tried the Colgate Optic one, but I've been using Crest 3D for about a year now, and I couldn't be happier with the result. It doesn't make my teeth very sensitive or turn them too bright white. I think it's the perfect shade, and it only took me a few days to see great results!