I have a Garmin 2820 on my LT and really do like it.
I have a 2008 goldwing with GPS from the factory. I added a Garmin 550 for the following reasons.
Lot of Garmins out there - and some others as well. Garmin seems to be in the majority, model depends on ones wants, desires, and checking account. Myself, I have a Garmin 2730 because I wanted the XM radio, and bought it when they first came out. No reason to change, but the newer ones have bigger readouts. Also have a 2720 for the car, same thing but no XM, (CRV has XM), and that was price driven - about $60 delivered from ebay. Carol has a 2610 in her car, transfered from her previous car.
Great looking installation.I also have the Garmin 550, but I did not have to install a filter and I have no alternator whine in my headset.
I use the navigation, XM radio, and the bluetooth for my phone, It all works great. I have mine mounted with the dash mount from www.goldwginggadgets.com I really like the heads up display this way.