I bought the Lowrance iWay350c. I purchased mine for several reasons. Its primary purpose is navigation when I travel for business. However, it does backup duty on the motorcycle. It is small, built in battery and a cigarette lighter adapter, but most importantly, it is skinnable. A guy out there has created a skin for it that allows you to use it with gloves on, a biig plus.
The iWay500c is waterproof, however, I am not overly worried about water (as I don't have mine mounted to the bike) and I prefer the smaller size (for travelling) of the 350c. Plus, the price was great.
Other features include a picture viewer, mp3 capabilites and feeding both mp3 and voice commands through an FM radio. Again, I liked the features.
I have a 2620, which is also a great device. A little more solid than the Lowrance. However, size was a consideration.
Alas, my Lowrance has had an issue. The hard drive failed (actually, I am not sure it was every really working). I called, and after a few minutes on hold, they are taking care of me. As I say, great customer service isn't what happens when everything goes right, but when things go wrong. I am impressed with Lowrance's service. Obviously, I would have preferred no issues.
I have no affiliation with ether company. I have two Garmin GPS's and one Lowrance. You can't go wrong with Garmin, but the Lowrance seems like more features for the money.