I have two units.
A hand held older model Lowrance plotter (no map ) that I used connected to a laptop serial port with Street Atlas running on the PC. Works great but takes up to much room.
I have the Lowrance iFinder Plus and the maping program that came with it. The map program is on two CD's and covers the entire US. I can load the iFinder with up to 128mb of data on a MMC or SD card the size of a postage stamp. It only works with the Lowrance mapping program.
Problem with the iFinder, it's to small and hard to see at night but it fits next to the door column on my truck and takes up no space.
It has all the mapping features of a full size PC such as find a hotel , street address ect.
The Garmin requires you to by area maps and I think it takes six maps at $75 to $150 each. Can't remember but it was having to buy all the maps and over time the updates that turned me off the other GPS units.
I think the best option if you have the room is the PC and Street Atlas.