Garmin and TomTom make the most satisfying portable navigation devices, says a recent J.D. Power and Associates study. They're the only two ranked above average. Magellan is just below average while Navigon and Mio are further below, according to the 2008 Portable Navigation Device Usage and Satisfaction Study. The navigation experience has improved so much that mounting is the biggest problem users face now, followed by accuracy of routing and address information. Other findings from the study:

-- Buyers want real-time traffic information, along with current weather forecasts and up-to-date gas prices. (What buyers really want is truly accurate traffic information but that feature hasn't been released yet.)
-- Brand loyalty is high: 90% of current buyers say they definitely or probably will buy the same brand again. That's one of the problems facing latecomers to the market such as Sony. High initial pricing didn't help them, either; Sony placed more of a premium on its brand name than buyers did. (Sony's Nav-U prices are now more in line with the market.) Panasonic Strada is in the same boat.
-- Half of current owners use their PNDs at least 1-2 times a week.
-- The typical selling price in 2008 was $245; a year ago it was $375. When buyers shop for a new unit, price is the prime buying consideration for 40% of buyers.
-- People who bought PNDs online were happier than those how bought in retail stores. No surprise there.

Actual scores (1,000 would be perfect) were: Garmin 806, TomTom 798, industry average 791, Magellan 785, Navigon 753, Mio 711. No other brands got enough responses to be rated. Power doesn't release the margin of error in its studies, meaning whether the 1% difference between the scores of the two leaders falls within the margin of error on the survey of 4,866 respondents queried in September. It does, however, provide Power Circle ratings -- one to five bullets -- where Magellan and TomTom got 5s, Magellan 3, and Navigon and Mio 2's.

To see a J.D. Power video discussing the study, , click here. To see PCMag.com's reviews of GPS navigation devices, click here.