NAVTEQ and TeleAtlas both provide mapping data to GPS manufacturers, online mapping services, and generally any other application that might need street-level mapping data. The conventional wisdom has always been that NAVTEQ is "better", but more expensive, and TeleAtlas not so good, but cheaper. Here is some more specific data:

1. In general NAVTEQ has more current mapping data in the United States. Want to see for yourself? Google Maps uses NAVTEQ mapping data, but Google's GMap Pedometer site uses TeleAtlas maps (no doubt the result of NAVTEQ's unwillingness to let Google use the open API).
   
   Now Check out a view of the same area of New Jersey via Gmaps (using TeleAtlas data) http://www.sueandpaul.com/gmapPedometer/?centerX=-74.03115749359131&c... , then checkout the same map using Google Maps (NAVTEQ): http://maps.google.com/maps?q=hoboken,+nj&spn=0.015104,0.027479&hl=en
   Clearly the NAVTEQ map is more up-to-date. Try it out yourself using your own address.
   
   
2. NAVTEQ is generally considered better, so why does anyone use TeleAtlas? No surprise here, TeleAtlas is cheaper.
   
   
3. When Google's Pedometer site recently switched to TeleAtlas data, it triggered a lengthy forum discussion about how much better NAVTEQ was. If you read through the postings, you'll see a lot of examples of data missing from TeleAtlas' mapping data in North America
   
   
4. In my own testing, I found TeleAtlas mapping data was less accurate than NAVTEQ on several occasions.
   
   
5. If popularity is any measure, then we can definitely conclude NAVTEQ is the better option: Google Maps, Yahoo! Maps, MSN Maps, and MapQuest all use NAVTEQ.
   
   
6. NAVTEQ is a US based company, while TeleAtlas is based in Europe. So while NAVTEQ is definately the better choice for North America, TeleAtlas is better for Europe.
   
   
7. I spoke with another expert on mapping data today, and he told me that TeleAtlas is improving their data every day, and it's entirely possible that TeleAtlas will someday be the better option. TomTom is the fastest growing GPS manufacturer in the U.S., and they're using TeleAtlas. Garmin and Magellan are using NAVTEQ, so clearly Magellan and Garmin have made a decision that the extra money for NAVTEQ is worth it. Of course, TomTom is a dutch firm, so for their European customers, TeleAtlas is a better choice.

One of the most common complaints I hear about GPS navigation is "it took me on a crazy route", or "my destination wasn't even on the map!". These complaints are always the result of mapping data, and really don't have much to do with the GPS unit itself (which is why I almost never point out mapping inaccuracies in my reviews, since all GPS devices using TeleAtlas or NAVTEQ will share the same mapping deficiencies).

NAVTEQ and TeleAtlas will both always have mapping inaccuracies. However, currently NAVTEQ is the better choice (in the USA). I think it speaks well for Magellan and Garmin that they are willing to pay for NAVTEQ mapping data. Frankly, when choosing a navigation device, I can hardly think of anything more important than having current and accurate maps! Until I hear otherwise, I say NAVTEQ is the way to go.