I've used only Garmin and am very satisfied with them.
Key features: Text to speech, Lifetime map updates, lane assist.
I recently drove my son's car and he has a Garmin Nuvi (not sure which model) that has lane assist. Very nice feature when driving in large metropolitan areas.
One of my GPS units has bluetooth for wireless connection to my phone. The microphone on the GPS picks up too much ambient noise and the speaker isn't clear enough and sometimes not loud enough. I don't bother with it and use an ear-pience instead.
mostly for my big weekend trips around America. Can anyone suggest the key features to look for and what are the good brands?