I have a Quest and a Streetpilot III. They're both out of production but still available new and are supported by Garmin. Prices are comparable. I prefer the Streetpilot for the larger screen. The Streetpilot is on a Touratech (065-0039) cradle RAM mounted.
http://www.cycoactive.com/gps/ttsp3.html
Touratech makes the same cradle with a key lock and also makes mounts for the Quest if you go that route.
http://www.cycoactive.com/gps/ttquest.html
Touratechs are popular with the BMW GS crowd for semi-off-road use but the GPS is securely mounted and easily removed.
The SP has a removable memory chip, Quest has what's built in. SP uses replaceable AA's, Quest has a built-in battery. Both can be powered from the bike (I have the SP hardwired), the SP with any power cord if you have a power outlet, the Quest must get power through a powered mount.
During a trip through Canada, the Quest did lock up. Had to wait 2 days for the battery to run down and reset before getting home and finding out there is a soft-reset key sequence (in the instruction manual I didn't have with me at the time).
Surprised not to see half-dozen posts from guys saying they don't use GPS and you shouldn't either, sure they'll show up eventually :wink: