One of the factors in making a decision is if you are going to want to follow a "route" and want turn by turn directions or not. Routes give you turn-by-turn directions, and alert you before the next turn. Following a "track" does not give you turn-by-turn directions or let you know a turn is coming or anything, you have to look down at the screen. A "route" or a "track" can be created in MapSource or BaseCamp and then pushed to your GPS unit via a USB cable or loaded into a small memory card. Not all GPS units can use routes or tracks. Some can do both, some can do only one.
Additionally, for those units that can follow "routes," some units offer audio output via a jack or bluetooth. Others make a beep as a turn approaches. Many riders pipe the bluetooth or output jack audio into their helmets, so they can watch the road instead of the screen. Units that merely make a beep may not have any means to output the sound.
These are just things to consider. They may or may not be important to you.
I started of with a 62C. It only beeped and there was no way to get audio into my helmet to hear the prompts. If you are in completely unknown territory and your route takes many turns, it may drive you nuts (and be less safe) to have to watch the screen all the time.
Eventual Master of the Obvious
2005 R1200GS | 2013 R1200GSW | SOHC4 208 | DoD 2032 | BMWMOA | BMWRA | YB