Which looks better on you? Light blue looks better on me than white does. White is best for formal occasions (like weddings, galas, etc.), but for meetings (which are not formal occasions) either is fine.
I prefer light blue, in fact I plan to wear a light blue dress shirt for my own wedding next spring (or a blue and white bangle stripe). The reason is that I cannot find any, and I mean any, white dress shirts, at any price, that are 100% opaque. This is important for me as I am not a huge fan of undershirts unless it is really cold out. This will be particularly true for my wedding, when it will be spring and I'll be in a three-piece suit.
As far as formality, I think it matters what the shirt is paired with, and how sharp it looks. The one time I think white is required is with a black suit. Otherwise, I think the following combinations are formal enough for any event which isn't black/white tie:
Grey with blue and white striped shirt with white contrast collar
Navy suit with light blue shirt
Blue suit (lighter than navy) with cream