Great question, and let me tell you how nice it is to have a good quality GPS onboard when riding in the back country.
There are three of us in our group that run the Garmin Zumo 550. Its designed for motorcycles, atv's etc. It is weather proof, temp proof, full color touch screen. It works great. We've been caught way in the back, and we literally drove out by zooming in on our track log, and driving by watching the screen.
We dont ride with out them now, I use it on the Rhino too
I have a garmin etrex for my mountain bike. it's small which is great on the mtb but it uses aa batteries and can lose the signal fairly easy in trees and from bouncing around. Tried it on the sled and motorcycle but needs a 12v power supply to be reliable.
I have the zumo 550 for my motorcycle and it's awesome. Lots of features but they're around $900 so a bit pricey.
I use a garmin rino 530 on the sled and the boat. The lithium battery lasts a very long time - 3 days or more on a single charge. If others have the same gps you have the ability to locate them or talk to them. This was very helpful on friday when my brother inlaw took a different trail up through the trees and we got separated. Lets you find people and you can tell if they turned around to look for you.
I'd recommend a gps with a lithium battery unless you can tap into power from the sled or atv. Then it comes down to the antenna. The rino hasn't lost a signal yet for me. A color display is also a lot easier to view.
3 of us have rino's so that's what I use on the sled.
Garmin is the way to go. I am a helicopter pilot and I use a Garmin 60csx for flying and recreation because it is a good off road gps(the c is for color, the s is for the barometer feature and the x is for the type of chip being used). It is very user friendly. The cost with accesories is approx $400. The zumo is also a good one as it is made for the elements but pricey.
Also a nice feature Garmin has is you can run most types of maps as a background. There are people that have the rights to program whatever kind of map you need. At a cost of course. Here in Grande Prairie we have the developer of PatchMap and he is possibly making up a recreation mapset that can have routable snowmoblile trails and boundries on it.
Few tips when buying
Garmin seems to have the most accesories
Color screens are a very nice feature
Rechargeable are nice but if they run out on the trail and you have no accessory power, they are useless. A battery model that uses AAs can easily be swapped out on the trail. My Garmin 60csx will run all day in the cold with a fresh set of batteries in the morning. Turned on in the morning and thrown in the top of the backpack so I can record my track all day riding. Hook it to the computer at the end of the day and you can print off elevations, speeds and distances. A sleds black box.
When buying, go to a store or dealer that has all the models on display so you can use it before you buy it. You might not like the button set up on some or features or screen size or etc etc.
Make sure it is water-proof, not just water resistant.
Me and several of the guys I ride with have the Garmin Rino 530hcx. Waterproof, colour screen, and also works as a 2/way radio w/ weather forecast. Best of both worlds IMO. I had the 60csx before and upgraded to this.
Garmin Etrex color, with topo map. I have it mounted to my sled through a marine mount.( swivel and tilt) Easy to use, accurate, good price. Lanyard throgh the raiser, rolled sled gps and mount no problem, Easy to view, quick toggle puts on the light. Sledding out my way fog can be a problem, ive lost the signal very few times. I don't go sledding with out it,
Six years in the area, fog, heavy snow and dark can make things look un-familar. Use it a lot when hunting.