Depends on the size/price/capabilities of the unit you are looking for. Most handheld receivers will give you "live" access to where you are on the trail, similar to your smartphone, with much better accuracy. However, a handheld GPS is only as good as it's mapping software. I know some others here on SCCX actually have a laptop mounted in their driver's compartment and use mapping software to track their progress that way.
Also, the Lowrance units that Steven has are great too.
Figure out what your application needs are (portable vs handheld, power needs/battery/12V), budget, space constraints, and poke around some of the forums to see what others use.
I have a handheld DeLorme PN-60 unit that I use for paperless geocaching. From a mapping standpoint it uses uploaded discs from DeLorme Topo maps which are very handy. I use a RAM windshield mount to keep it from bouncing around the front seat.
It is very accurate, sometimes down to +/- 7 feet, although all GPS feature a 30 ft. range of pinpoint accuracy.
It does eat batteries, so I use rechargable AA's and keep a few extra handy just in case.
A day of geocaching, around 8 hours, will leave me with about 25% capacity. There is also a 12V charger kit that plugs into my power outlet in the Xterra.
I have owned both Garmin and DeLorme units. The Garmin was much more user friendly out of the box, but my first unit crashed and burned the firmware and never came back. The DeLorme is a more complicated ramp up to learn, but I really like its durability and quick upload process for paperless geocaching.
Max Powers would also be a good person to hit up about GPS questions as well.
