It depends on your job, man.
As a dismounted signaller, I have a Garmin Foretrex 101. I took the wrist strap off, attached a 550 dummy cord, and I keep it in my pocket and tied to my belt.
- Unlike the newer 201 and 301 models, the 101 runs off AAA batteries. I never have to worry about charging an integral battery in the field because I just ADREP fresh ones.
- The trip computer can be customized and is very user friendly. You can set it up so that your grid, bearing, and time to destination are available at a glance.
- It's very small and therefore convenient to carry on you all the time.
- It's a very streamlined GPS. It has the bare necessities of functions, easy to use and set up. There is no electronic compass, but a GPS can't replace an old school magnetic compass so you'd be carrying both anyways.
- I used to have a more capable Garmin Vista, but I prefer the Foretrex for the above reasons.
Maybe if you're a LAV CC you'll want something more elaborate with colour and maps, but for a dismounted guy looking for a fast and light nav aid, I don't think you can beat the Foretrex 101.