I wrote the following a couple of years ago for the COG web site - it is pretty much current in terms of what it suggests, though obviously models, features and firmware have changed a bit. These days I STILL prefer the 276/376 etc . . . but I also own a Zumo 550 - I have reviews of both posted at epinions:
Zumo:
https://www.epinions.com/content_406049689220
276c:
https://www.epinions.com/content_147941396100
I vote Garmin . . . and I prefer the 276c for reasons spelled out in the Zumo review. However, if you are planning a 'grand rounds tour' of the US, and if you aren't bringing a laptop, the tracklog on Zumo will carry your entire trip in addition to interfacing with your cell phone and providing music.
The quick of it is that Garmin uses (and for the forseeable future will continue to use) Navteq maps, while TomTom uses TeleAtlas. Canadian maping is from DTMi and the Canadian government for both.
Navteq maps are better in North America, while TeleAtlas' maps are better for Europe. Since TomTom bought TeleAtlas, you aren't likely to see their maps on a Garmin unit. However TomTom does offer online map updates where Garmin goes for annual releases. Then again they don't build all THAT many roads.
TomTom also allows you to download custom voices (such as John Cleese) if you have the extra cash to burn for such nonsense.
Here's the content of the original post:
ZG-GTR fanatics - Buying a GPS
I got my first GPS when I got lost in New Hampshire - at the end of a 2 lane road, out of sight from all civilisation and running on reserve. I had maps with me. Maps are nice, but to use them you need to know where you are and I didn't. So I resolved to get a GPS unit if and when I got back to any sign of humanity.
I did, and I followed through.
After doing ALL my research I decided that two or three key features were necessities:
1. SUNLIGHT READABLE AND HIGH SCREEN RESOLUTION
My first unit was the then state-of-the-art Streetpilot-III. It had a great contrasty display, but limited readability in bright sunlight. Squinting at a screen or trying to shade it so you can see where you are while tooling along at 70 mph isn’t pleasant.
2. LARGE TRACKLOG
The tracklog is often overlooked - it is the function that tracks where you've been and when. From the tracklog you can derive your location at any time along a route you've driven and from that you can infer the speed travelled and such. A larger tracklog stores more data - it takes about 10 points per mile, depending on terrain - so a 10,000 point tracklog is good for about 1000 miles and that's a good thing.
Automotive units with the exception of the Quest have small 2000 point tracklogs (the Nuvi, c & i series units have no log at all), so you can't even capture a whole day's riding. The lower end units from Garmin and other have no tracklog at all.
Why do I harp on tracklogs? Because they are useful - they allow you to find that really neat section of road at the end of the day and plan your next ride around that if you wish. They also allow you to replay a situation - I used mine to beat a speeding ticket - that alone paid for the GPS!!!.
3. WATERPROOF
Need I say more? Not all units are waterproof
4. BATTERY OPERATION
There's nothing like being able to pop the unit off the bike in case you want to use the unit for something other than a wired-in scenario. Because I had yet to install my fuse and power distribution panel I was riding the FJR and running my unit on its rechargeable batteries, since it will run 15 hours between charges. What if I broke down and decided to hike cross country? Having the GPS to guide me is a significant plus (Quest is the only truly automotive unit with batteries).
5. MEMORY
Many of the latest navigators now come complete with the entire of North American roads (Or European ones, if you buy that version) pre-loaded - a very good thing. But DON'T BUY A UNIT WITH A HARD DRIVE IF YOU PLAN TO PUT IT ON A MOTORCYCLE. Also stay away from a unit with an internal gyroscope.
NOT having all of the dirt tracks in the Rockies if you are an east coaster and plan no visits to that part of the country isn't a hardship - and even the smallest of the newer memory units will carry more road than you can ride comfortably over several days - and where the unit has removable memory (like the 2610 or 276c) you can always load up several chips if needs be and plug the right one for the day's ride, so no PC is required - though if you want to record the trip (see tracklog above), you'll need the computer anyway . . . so memory (or it's lack) becomes a moot point.
6. OTHER STUFF
You can now get units that have traffic information (in selected markets), weather radar displays and have MP3 players and XM radio receivers all in the same box - some have Bluetooth support, though you'll need an intercom system for your bike to make use of the sonic properties of your navigator.
For my part I carry an iPod for music - I suppose I could dump the XM into the tank bag, but I do NOT want everything in a single unit. For one thing I have one XM subscription and I want to leave it that way. Using an iPod means I only meed to manage a music library in a single device. Garmin for some reason limits you to 500 songs (since written, this has been increased to 1000) - I have some 2900 in the iPod.
7. SUMMARY
For MY money, I'd get the 276c/376c/378c/478c (as your needs dictate) from Garmin. Actually, I have a 276c on the bike and another in my car (wife wouldn't use the one I bought for her car, so I grabbed it for myself).
This wasn't an exhaustive analysis, but let me say this - On the day I wrote this article we were out riding in upstate New York. We had trouble getting across the border (high alert, long lines to get across). The GPS helped us find a crossing that NO ONE knows about. The poor lonely guard had cobwebs!!
When we started home we had some time to kill, so I told the unit to plan the shortest (not the fastest) way home - I then proceeded to ignore the directions, using the map display to find roads that had both ends connected to *something* and off we went . . . Three hours of VERY interesting riding that took us all over the place - in and out of the Adirondak Park - we didn’t do our usual speed-fest at 100+ mph (actually we ran at about 80-90 most of the time, but that's what happens) and having the GPS meant that I had an idea of the way the road stretched - whether the upcoming turns were tight or not and that allowed me to anticipate my line around blind corners better.
My riding buddy (K1200S) told me he found the afternoon run more enjoyable that his usual 'blow around the corners with sparks flying from the pegs' riding routine.
When it was time go head home, the unit had already determined the shortest route (which means some of the better riding, because otherwise it wants to superslab it home) AND IT HAD A PROJECTED ARRIVAL TIME, CONSTANTLY UPDATED AS WE RODE. So we knew when to start heading home . . .
, but not happy with the services 
