From what I've seen...
Mapquest has the most up to date pictures
For many areas. Our home is in a new community that is 4 years old. On Google Maps it only shows 4 of the the 68 houses in our immediate neighborhood. Mapquest shows all of the houses. It had our address labeled as three houses down and in the middle of the street, but hey you can't have everything.
Google Maps and Bing's pictures are older (for instance, google and bing still has the wing in their pictures where BLT currently stands) but the thing I really like about Bing...you can switch from Aerial to Birds Eye view, and they have terrific pictures at that level (albeit older)