You raise a good question. One to which I have no clear answer.
My Spyder came with a Garmin 590. I updated the software to that found in a 595. (Easily done. Search the interwebs) The mount was at the center of the handlebars; a terrible location, requiring a downward look to see what it's doing. I moved it up in line with forward view. A hassle.
the Garmin software is, uh, poor, to put it nicely. I find route planning with Garmin to be more trouble than it's worth. So I plan elsewhere, convert to a GPX file and import into the Garmin. That works fairly well, but far from what I want.
On a recent trip, I found the Garmin's ability to find locations to be poor to nonexistent. YMMV, of course. I was looking for not very common roads and places. Its database contained few of the places/roads I sought. Other GPS apps (see below) did.
I've tried a bunch of GPS apps on a phone. Download app, download its maps. Most are better than Garmin, which is damning with faint praise.
I was a Sygic user for a long time, even bought the App to use on both iOS and Android. They keep adding "features"; too many features to make it clean and simple to use. I've tried Waze and a few other apps.
Finally found OSMand, which of all the apps I tried, is the best.
At the end of the day, I use a paper map. Most states will send you one for free (go to the state's tourist info web site and fill out the request form. Heads up: Washington state hasn't had a paper map since, I think, 2009. I've kept my copy. All the states around Oregon send me maps, and I've found they do what I want.) The Garmin is still there, largely to compare the speedo with the GPS' speed reckoning.
I probably won't be around to see it, but my impression of GPS technology for end-users like us is that it's a technology still in infancy. Maybe another decade of development will see a mature product that actually works and works for the sort of traveling real people do in the real world.
We'll see.