I have the Garmin eTrex Legend. Look for something with a stronger antena. Don't get me wrong, I like the thing ALOT. If it could get a better signal I'd be in love with it. If you are on a trail or in clearing, you can get a sounding as to where you are. Once you are under tree cover though... all bets are off.
The Legend is the most basic model they make. So I would think the other units have addressed this issue. Also a color screen would be very helpful, if you can afford the ones that have them. There are tons of reviews online for this kind of thing though. If you find a particular model appeals to you, google the model and "review" and you'll get a deluge.
Garmin's features and software are excellent. Be sure to buy a "bundle" of the unit and software. You'll get a set of topo maps of North America and city guides. I really enjoy both.