Shane,
Like Buzz said you could be happy with either unit but I too prefer the Garmin. As a total package they are the leader in this particular industry. The Garmin units are a bit more user friendly and the new Magellan units are difficult to use especially with gloves or larger fingers. I am a Professional Land Surveyor and have a background in Geodesy so myself and my crews have used almost everything out there for the last 20 years. We have very strong opinions about equipment like this because we use it so frequently. Handheld units are very useful for a number of applications since "Selective Availability" has been turned off. Many units will talk about +/- 1 meter accuracy but you'll find that to be more like 3 meters repeatably which is typically adequate for the intended uses. You may occassionally come within 1 meter of a previous waypoint or a known point but not most of the time.
Let me also provide you some background about coordinates. You'll be best served if you utilize geodetic coordinates which we commonly call Lat/Lon. The basis of all Cartesian cooridnates is Lat/Lon. UTM, state plane, etc. are all Cartesian coordinates calculated on flat planes at some elevation below the surface of the earth. Northings and eastings are calculated on flat planes and a flat surface can only approximate a curved surface such as the earth for short distances. That being said there are 60 UTM zones and probably hundreds of State Plane zones in the US if you were to count them all. There are 4 in Wyoming, 3 in Montana, 3 or 4 in Idaho, etc. Wyoming exists in two UTM zones and so does Montana and Idaho. Therefore you have to know where you're at and what zone to have your unit set in. The further you get outside of the zone the more exponentially the coordinate error increases.
The best way I can explain planar coordinate error potential is by visualizing an orange peel. A small portion of that peel can approximate a flat surface. If you were to take a plane and cut through the orange peel the peel would intersect the plan on opposite sides. Those intersecting points are the limits of your UTM or SP zone. If you try to work outside of them your error increases drastically. If you were to try to flatten that orange peel it would start to stretch and rip apart more and more as you leave the intersection points. That is distortion or error potential which is why there are so many different zones. The UTM zones are so large however (6°) that they have an error potential of 1' in 2500' within the zone. Not enough to worry about for handheld units but unacceptable by land surveying standards. We utilize units that cost in excess of $60,000and are capable of measurement errors of 1:2,000,000 or so. To get accuracies like this you have to set up over known points and have more than one unit running so that you can differentially correct or post process.
State plane coordinates are on a calculated on a plane at approximately sea level and UTM coordinates are on a plane that is approximately 5500 feet below mean sea level therefore they are also the least accurate cooridnate system available to us. Handheld units do not contain the complex software routines necessary to differentially correct positions, or project to your elevation so the further you get toward the mass center of the earth from where you are at, the less representative a distance is between two points. A wedge is the best example. The tip is the center of the earth. A planar surface is somewhere in the middle of the wedge and you are at the exterior end of the wedge. The distance between the two endpoints of the wedge is longer there than measured in the middle of the wedge where the cartesian points are being calculated. That is why even though UTM is a popular system it is the least accurate available to us.
Sorry to go so far outside of the question about recommended units. As a land surveyor I try to educate people every chance I get so that they understand what we do and can hopefully better use their equipment. Geodesy is the foundation of GPS and coordinate systems and most people and even a good number of surveyors don't understand this foundation before utilizing their equipment. If you have any questions or would like to understand a little more I can recommend a couple of very good online tutorials that explain Selective Availability, Trilateration, Ellipsoids and just how everything works in general.
Easy for me to ramble on about geodesy and GPS as I have been using it and teaching it for almost 20 years now. Being charged with protecting the public I always feel like I need to help educate the general public for free whenever I can whether they are ordering a survey of their land which is valued at $5k and acre or just using a unit recreationally. Some find it interesting and some just don't care. I feel good about sharing when I can though.
