I like them all, white because it's so different (I usually use/wear dark colours) and bright, grey because of it's metaphorical-ness (Things aren't always black and white ) and black because black. And that's the best reason there is.
All. Actually all of these are beautiful in their own way. But I chose black because it looks great with every other colour (except for dark blue and brown maybe. I don't like that.) And my beloved bag is black but there are soooo many buttons on it (it's 25. I counted them.) you can't see it anymore. But in summer white is better I think and it makes a nice contrast to my skin because I then look like I came from Spain or so xD If there were any other colours I'd have picked purple.