I've been using a Garmin 60 with 24k Topo maps (which are routable). I'm saying it's the "best" but I've been happy with it - also use it for street riding, on my mountain bike, and as a handheld while hiking. Thinking about upgrading to the 64.
I like the 60 series and the Zumo 665LM with ext. antenna. https://buy.garmin.com/en-US/US/on-the-road/motorcycles/zumo-665lm/prod120318.html
Garmin 276c for years and last year I dedicated my old Samsung S3 to GPS duty with Locus Pro loaded and offline vector maps installed. It rocks.
My very old Garmin Nuvi 215W on a standard handlebar mount, powered from waterproof USB socket works well enough for me. Philippines OpenStreet Maps loaded directly to the SD Card, very accurate and regularly updated for free.
Garmin 478 is my go to when I want to zoom in on forest service roads and excruciating detail. I hold onto it as Garmin dumbs down the interface version after version. Riding my road bike and wanting to integrate a bunch of audio sources..it's a 590LM. I wish the 26xx, 27xx, or 28xx interface was still around though. I miss it.