What is your budget?
The Zumo is great for motorcycles, but still $500 or more. I have the 550 and a Nuvi 760. I've owned the 2610, 2720, 2820, Quest, Nuvi 360, Nuvi 660, and Nuvi 760 (and some handhelds). Before I bought the Zumo, I used my Nuvi 660 in the map pocket of my tank bag.
If your budget is tight, some folks are going with the old Garmin 2610's or 2720's. Others are buying one of the low-end Nuvis, like the 200 or 250W, available new for $200 or less.
Comes with great mount
Easy to work with gloves
Can share routes with SD card
Customizable front screen
Less than $200
Can optimize route with multiple destinations.
Doesn't have GarminLock
No internal battery, high sensitivity receiver.
Not considered "motorcycle friendly" by Garmin - or waterproof
Large, bright display.
Can't display speed and map at same time if route is selected.
Most models can only contain one via point and one destination on route.
Has internal battery, useful for walking or biking.
Has high sensitivity receiver, recalculates quickly.
Some models have internal antenna
Some models have bluetooth, FM traffic support
2005 DL650 (sold) | 2009 DL650A (sold) | 2008 Tiger 1050 ABS | 2012 WR250R | 2008 CRF100F