I have a Garmin 2610 (big and heavy, but awesome!) and initally used it in Garmin's own motorcycle bracket, with a Ram arm - which was fine and the vibration acceptable, although I found that after three weeks of high speed dirt road riding, (presumably the vibration) had cracked the casing around the adjustable backplate pins on the GPS - due to the way the unit clips into the standard bracket.
I therefore tried the Touratch mount which cradles the unit, but found the MvG version (with the foam pads) while great around town, vibrated so much that you couldn't read the screen over 50mph even on tarmac...
So I now have the Ram cradle (on the Ram arm), which seems to be the best of both worlds - it cradles the unit completely, and doesn't vibrate excessively at highway speeds...
Oh, and if that wasn't enough, it only cost £8.99!