I like Garmin's units the best. I have a couple older marine hand helds and my dad got one of those slick new Nuivis or something close to that. What do you want it for? Highway/road use or offroad/marine/hunting type?
I use the TomTom Software with my Treo Palm pilot. Love it. And since its a phone, I can call the destination (it has a complete phonebook built in) to make reservations/ask questions.
My GF has a Magellan that is pretty nice, but it just a car mounted one.