A durable, weatherproof, and rugged model is a must. At first glance, a touch screen might seem like the best choice, and it would be if we lived in a vacuum. However, weather and conditions will sometimes bring mud, grime, and dust to contend with which can make it difficult to view and navigate the screen, plus you might scratch the screen when your gloved or ungloved fingers interact with it. By the same token, if you’re a rider who leaves the bike in the garage in any of those conditions, it’s not such a negative factor. Suffice it to say, some riders would be better suited with a device that has buttons next to a screen that’s easy to see and manipulate to navigate through all the unit's menu features.
The natures of mountain biking and road cycling are different. Out on a trail or bushwhacking through open terrain like you might find in Moab would necessitate the best mapping features presented on the screen, crystal clear and in real-time. Some models zoom in and out a lot faster than others. Mountain biking enthusiasts would also greatly appreciate a built-in altimeter. Generally speaking, road cyclists tend to have sport and fitness goals high on their list, so they like the best features to monitor their heart rate. (Although most models have heart-rate monitoring capabilities, the actual monitor is sold separately.) Also of interest to them are monitors for calories burned as well as pace (cadence) as it relates to the mileage they're putting in.
The models below that emphasize those features, traditionally characteristic of a ‘cycling computer’, but without extensive mapping features (more like the original GPS models), might be best for them. Those models are still capable of indicating where they are and navigating to where they want to go, but they key-in on displaying what condition the rider is in to target fitness goals. These cycling enthusiasts might also prefer a GPS unit that’s strapped to the wrist rather than mounted to the bike so that it can be used for running and other non-bike-related fitness activities. Check out the Garmin Forerunner series for something like that. No matter which type of cycling you engage in, you want long battery life and preferably standard batteries you can change out. Charging rechargeable batteries well into a ride is not feasible.
With these things in mind, let’s now point out some of the best cycling GPS mountain biking units below, with convenient links to pages where you can learn all the specifications. You can purchase one when you’re sure you’ve matched your preferences to the worthiest device for them. The prices listed below from Amazon.com are, of course, subject to change but should give you a fairly accurate ballpark number. Use the enthusiast forums and cycling websites to see what real users are saying about performance, as any site that wants to sell you one will leave out the drawbacks of a particular unit.