Thanks, Chris, It seems that Furuno wins the service and support award despite being slightly more expensive than the others. That's worth the extra expense in my opinion.
I've been pleased, but then again we switched to Furuno on the previous boat in 2009-ish when "time zero" (I think perhaps referring to instantaneous screen refresh) was first becoming a thing... so by now, it's what I'm used to and I don't have too much recent experience with other makers.
The Cetrek plotter that came on that boat more often took 3-½ days to redraw the screen, and Cetrek disappeared anyway...
The early Garmin support for their systems on this "Heinz 57" boat was decent, but then I found they also charge for annual chart updates... unlike Furuno's older NOAA chart system with free annual updates.
(Not sure how Furuno updates for the optional paid C-Map charts worked; didn't have those. Also, not yet sure how the newer Furuno/MapMedia charts -- I think maybe only available in the new XL systems, newer than ours -- will be updated. Our recent TimeZero laptop upgrade came with both charting systems, user selectable, so I'm guessing there's some carry-over like that to the new XL release too.)
More recently, I've asked Raymarine a couple questions while we troubleshoot an actual glitch on our controller and as we looked into maybe improving our Furuno MFD-Raymarine AP interaction. (Remembering that Heinz 57" thing.)
Both times, decent answers. Ref the glitch, they recommended having the existing unit repaired, and they explained why. Ref the potential improvement -- which I thought might have involved sending feedback from AP to MFD via NMEA0183, via a translator to NMEA2000 -- they opined no significant improvement, don't spend the time/money. Both answers, decent enough. During all that, I saw there is (or at least was) a Raymarine forum online somewhere too, although I didn't happen to see anything already posted that would have been relevant to my questions.
Anyway... all this amplification in case useful...
-Chris