A navigation system is a complex device, and there are many details to consider when making a purchase. To make our results as clear as possible, we organized our research results into these categories:

• Display and controls

• Maps and journey planning

• Traffic, speed cameras, and other information

• Communications and ease of use

• Price

The most popular sizes for a navigation system’s display are 5", 6", and 7". However, models as small as 3.5” are widely available. Is screen size really a significant factor?

Most people with average vision find a 5" screen quite comfortable, but that opinion changes if the unit is mounted in a larger vehicle, such as a van or RV. Dashboard layout and driving position in those vehicles cause the navigation system to be mounted farther from the driver’s eyes than in a smaller sedan. A 6" or 7" model would be a better choice. The latter are particularly popular with professional truckers.

On the other hand, a big-screen GPS may not be the best choice in a compact or subcompact car. A 7” display in a smaller vehicle might seem to block too much of the view through the windshield! If possible, test drive a navigation system with your car to determine which size display is best for your situation.

Screen clarity depends greatly on display size, but clarity is also affected by resolution. Older models deliver 480 x 272 pixels, while many newer ones offer 800 x 480 pixels. That pixel density can make a big difference.

Some owners complain that bright sunshine decreases visibility on a particular model, or that the screen is too reflective. Reviews can also indicate that a model isn’t bright enough. Changing the mounting angle of the screen often resolves these issues. Models that offer a night mode automatically adjust display contrast for better viewing in the dark. Before selecting a navigation system, check whether any display issues are indicated frequently across a significant number of customer reviews.

Touch screen control has always been a feature of satellite navigation systems, and some models now offer a pinch-to-zoom function. However, on-screen controls require you to look away from the road and take a hand off the wheel.

Several of our top choices mirror smartphone and tablet technology by offering voice controls. Voice command can be safer than touch screen, but responsiveness and quality of the voice control system are very important.

GPS data is updated constantly. Big cities have more detail than rural towns, but mapping of even the most remote areas is getting better all the time. Also, areas that are thoroughly mapped change frequently, hence the value of lifetime map updates. You might save a few bucks by not having this feature, but for us it's a no-brainer. All our finalists offer it.

However, downloading updates can be frustrating. Many owners find the process painfully slow, and on some models, we agree. Occasionally updating is impossible because the navigation system lacks sufficient memory. Manufacturers are working to correct and prevent these issues with each new model, but it’s still worth checking before selecting a navigation system.

Map display style varies between models. One useful feature that has become standard is additional lane guidance on a split screen when approaching an off-ramp or interchange. 3D technology is also being more widely used, providing a more realistic view of landmarks and surrounding buildings.

Actual route planning is also now available with many models, a major benefit according to the feedback we've received. Also, the sophistication of route planning preferences is increasing. Older navigation systems obliged you to choose to use freeways or avoid them; now you can mix and match to suit your preference.

Another popular feature is the ability to simply tap the map to select a destination, rather than typing in an address. It's particularly useful when you want to visit an area but don't have a precise location in mind.

POIs (Points of Interest) are nothing new in navigation systems. POI importance varies from one owner to the next, but this feature can be extremely useful when you suddenly notice you're low on gas.

Each manufacturer claims their POI functionality is better than the competition, but in truth there's little difference between them. The same is true for live traffic information. It's a great feature to have, helping you avoid serious roadblocks or major delays, but the key differentiator is the availability of the feature, not the quality of the information provided.

This wealth of live information seems tremendously useful, but most of these features are only available by connecting your navigation system to your smartphone. It's not hard to do via Bluetooth, but many owners feel the use of two devices is a bit of overkill.

Manufacturers are constantly adding new types of live information to their navigation systems. You can be alerted to a sharp bend approaching, a school zone, speed camera, even speed bumps.

Some models provide weather information, or a warning that you've been driving for too long and ought to take a break.

Roadside assistance is available through some models, and you can even get help finding a parking space.

We've already mentioned the option of voice control on some navigation systems. Whether finding your destination or locating the nearest coffee house, voice control allows you to keep both hands on the wheel and can increase safety. Voice recognition isn’t perfect, but the technology is improving rapidly.

Driving directions from the navigation system are also becoming more user-friendly. Manufacturers attempt regularly to make the navigation instructions sound more conversational. For example, the system might point out that the next turn will be at a light, or it might suggest stopping at a recognizable building. Older models tend to employ a “next left, next right” style of directions.

Some modern GPS models take the Bluetooth and smartphone link further. They act as a hands-free display when receiving a call. You can see who's calling and decide whether or not to answer. They can also display text messages.

We don’t recommend navigation systems under $50. The quality of information in these models will be lacking, and feature sets will be small. Maps may be poor with few, if any, updates.

A top-of-the-range model costs more – around $350 at the upper end – but for that price you get the most important features, including lifetime upgrades. These models are well worth the investment, particularly if you travel frequently to unfamiliar places.

When it comes to electronic gadgets, we're always tempted by the latest model. Each new release promises so much more than the last. But is that really the case? Our research, combined with customer feedback, resulted in a simple answer: it depends.

Some consumers love to get fully involved with their devices. They explore all the ins and outs, familiarizing themselves with every feature and capability. Others just want to turn the GPS on, enter an address, and follow directions.

The two leading manufacturers, Garmin and Tom Tom, cater to both groups. And the features they offer, plus the strength of their map data, really put them head and shoulders above the competition.

Garmin Nüvi and TomTom Via are both well-established, popular, and trusted by tens of thousands of users. These models are excellent choices for those who simply want to get where they’re going.

Garmin DriveSmart and TomTom Go are the next generation, already advanced and getting better all the time. With more features to explore, these models appeal to electronics mavens and people who like to get the most out of their gadgets.

For the moment, we feel the Nüvi and Via ranges have the edge in terms of price and performance, but it's a close call. Each product in our product list is an excellent navigation system.