I prefer MapQuest, mostly for a single reason
We moved into a new subdivision several years ago, so new it didn't appear on any of the map tools. MapQuest was the first one to show it, after about eight months. The Google Earth photo of my neighborhood is more recent than those of MapQuest or Bing (about eight months old), but I use maps more than satellite photos when I need directions.
Unlike some of the other respondents, my choice is based on the tool I use on a full sized monitor via a web browser, not on usage on a smart phone or dedicated web app. I usually print copies of maps before I leave the house. I find those easier to follow than relying on voice directions, since I can study the whole route in advance. Often there's enough detail to find ways around unexpected obstacles.