For my boat, Garmin gets my vote all of the time, everytime. Super reliable, rugged and easy to use.
I have a Mio Knight Rider GPS for driving.
http://www.amazon.com/Mio-Knight-4-3.../dp/B001DESTGO
It gets lost at times and not as up to date as the one on the Iphone, but having the greetings and turn by turns in the computer voice of Knight Rider is a lot of fun! You can program it to use your name instead of the default Michael greetings.