I have a Touring Plus for cycling. It's a neat little unit and does what it should do but I wouldn't use it on a motorbike mainly because of the screen size (I use a Zumo 660). One disappointment was that the unit only seems to be supported by Basecamp (which I hate) and not Mapsource (which I know well and has always seemed very logical to me). This is making me consider getting rid of it.
I used to use a Quest 1 on both motorbike & cycle and got on pretty well with it. The problem is the Quest didn't charge through the mini USB socket. The claimed battery life figures are always nonsense so for a day's cycling, I use a "Pebble" type battery backup, usually to give the Sat Nav a boost at lunchtime but this wasn't possible on the Quest 1, otherwise, I would probably still be using it.
I have tried to get to grips with Basecamp a couple of times and failed. If I get to the point that I can no loger use Mapsource, I'll ditch Garmin completely. The new Samsung Galaxy S5, being waterproof, looks an interesting option.