Navteq's map data is arguably the best and most up to date data commercially available. They have street level GPS for major cities in most countries, and just about every street in the US. You'll find their data sitting behind many of the commercial GPS offerings, and behind in-built systems from Ford, Mazda, VW, Audi, Jaguar, Porsche, Volvo, Lincoln, Maserati, BMW and Mini. Their data is _very_ good.

With regards to map errors - most if not all maps have them, some deliberate. It's a way to prove that someone else copied your map and passed it off as their own.