The new models are so feature rich now and yet the prices have come way down. The key features I would consider are the models that show how many exit lanes or turn lanes there are so that you can be in the proper lane; a unit that has text to speech for the street names (missing in the 2011 Mercedes Comand) makes it much easier to drive by ear than eyes on the screen.
Don't forget to get the most current data . . . Recalculating!