If you're looking for a GPS that calculates routes (road) on the fly, pay particular attention to the units recalculation speed. I have an older Garmin V model, and if you miss a turn in a tight area (like a downtown), by the time it's recalculated a new route, you've already missed that next turn, so it recalculates again, you miss the NEXT, turn, etc. Pretty worthless. It's fine if you don't miss any turns or you have a long distance between turns.

My wifes GPS cellphone does a much better job at tight city navigation. One, it speaks to you. Two, the recalculation of routes is much faster than the Garmin V. Three, you don't need to update its maps. Four, it's a lot cheaper than a dynamically recalculating stand-alone GPS, and does more stuff.

For trail navigation, I prefer map and compass. But I usually take a GPS along to verify my coordinates. I rarely need to navigate anything, mostly it's just practice with the map and compass that I do while hiking, and I use the GPS to "grade" how well I did with map/compass.