There are many ways to skin the GPS cat. The most important question is what features are important to you, and how do you intend to use it.
IMHO the very most important feature for a motorcycle GPS is it must have a means to get the GPS audio directions into your helmet headset. This can be by bluetooth ($$$), cables to some sort of wired intercom ($$) or even just some ear buds plugged directly into the unit ($). Thius requirement rules out many of the GPS units deigned for automotive use.
The second most important feature (to me) is the ability to upload and run routes. Whether it's just heading out on a day ride, attending an organized rally with group rides, or going on a week long vacation ride, I like to have routes mapped out in advance and just follow them. I do not like to just select a destination and let the GPS tell me how to get there, because regardless of whether you select Fastest Time or Shortest Distance these will typically be less interesting roads than the ones you can preselect and put into a planned route.
The next most important feature to me is a bright display that can easily be seen on the bike in direct sunlight. This can be a big problem as on a bike, even with a little display hood, the screens get washed out by the sun very easily.
There are many, many more features and functions that may be more or less important to you personally. A while back I did a full comparision / review of the two most popular motorcycle GPSes that I owned at the time,
Garmin's zumo 550 versus the newer zumo 66X series. You should read the details in review and form your own conclusions, but the executive summary for me was that I sold my zumo 660 and bought myself a second zumo 550, as I find that to be a superior unit
for my needs. Nothing has changed from that time to alter my analysis. Your final conclusions based on your own requirements may be different.
