I depends what your expectations for the GPS are. Garmin is by far the most prevalent motorcycle GPS out there and top notch customer service for when you get into a jam. That said, do you plan to create routes in a mapping program and then send these to the unit or simply want to be able to find and go to the nearest seafood restaurant. ( I am probably gonna hit Gloucester MA this weekend so have seafood on the mind). If you want to plan routes you and purchase a Garmin unit, there are 2 mapping programs available. Basecamp the new one and MapSource (which I use).
If you don't plan to create routes, but want to send some locations to the GPS, called waypoints almost all over them will accept them. Look at the specs for the unit and see how many "Waypoints" it will accept.
Now you may think you want to plan some routes to hit those special roads you see on a map there are 2 choices in the Garmin line. Zumo and Nuvi. The Zumo units will do everything you want it too, routes, waypoints, send routes to the unit and then some, water resistant, and motorcycle friendly.
The Nuvi's will do exactly the same thing as the Zumo. I have been running 2 Nuvi 1490's in all sorts of weather for the last 4 years and they work perfectly fine. Yes I run 2 gps's at once. With that said, in the Nuvi line you need to look carefully at the specs. If the specs refers to
"Trip Planner", you will not be able to download routes and execute them successfully !!! I have provided a spec that has trip planner in the specs.
Qualifier . this was true about 2 years ago when I purchased a 2735 at a great deal. I called Garmin and they confirmed it would not execute a route the way I wanted it too. The qualifier. This may have changed and maybe someone here can update. This unit was worthless to me for motorcycle travel and sits in the car to find addresses and stuff.
I have uploaded a pic of the Zumo 660 to show the difference. See that it take up 20 routes, but there is no reference to Trip Planner. It is my sense this is what you want to see under a Nuvi for effective route planning
The Zumo's have come down in price so they are within reason GPS City has the Zumo 660 LM (lifetime maps) for 365.00 which is a far cry from the 600+ dollars they used to be.
So if you can describe how you want to use the unit a more precise answer and unit can be found.
Willie