Think of buying a GPS like buying a pistol. Match it to it's use.
If I were taking another road trip (probably another cross country trip
coming this summer!) I would get a mapping unit with a car mount. Nice!
Geocaching and trail use? What is the point of a road map?
Dual use? Yup..... some do that fairly well.
I like SIMPLE. That's one feature I like about my M+P. As I was explaining to a lady and her family at a gun shop counter while showing them my M+P 9c, it's SIMPLE. Load it and pull the trigger, it goes bang. Don't pull the trigger, it doesn't go bang. No bells, no whistles, it just works for what it's designed to do. The safety is between the users ears.
GPS units can come as loaded with bells and whistles as any pistol out there. Best bet is to spend some time on geocaching.com in their forums and see what people are using and why. Just like here, you can bet they will howl like a stuck pig when they have an issue with their technology.
Use in a car..... it needs a screen you can read at a glance without
taking your eyes off the road for long. Reality is... you *should* pull over to use any GPS without a voice feature. Trail use can make do with pocket sized and small screen.
Take note of how many features they come with......
My experience is this: I used about 10% of the features available on a base level stock unit. My Garmin GPS 12 would do many things I just had no interest in. On the other hand it was fairly simple and I could work the controls by touch without looking at them. It also had good screen resolution and usable screen features (read that as large pointers visible at a glance without fussing).
For a car unit battery life is moot, but for a trail unit it's critical. I would
avoid a rechargable unit if possible. Carrying spare batteries is easy, carrying a house along to plug into is not. The military avoids rechargable anything for a reason. Several hours of constant use might seem like a lot, but once you are walking a trail it goes fast. The more features (color screen, ciggy lighter, wi-fi, whatever) the faster the battery dies. One feature I liked on my old GPS-12 was a low power use setting that sampled every five minutes rather than non-stop.
How tough is it? Is the case built to be dropped? Is it water resistant?
(Rain happens, ya know?). Does it have a built in light for the screen?
(Night happens, ya know?). Does it have a compass that works without the unit in motion? Exactly how accurate will it be with how many sats to look at? Under 5 meters is good for geo-caching. Closer is nice but not needed. We ain't aiming missles here.