Everyone will have their preference.
I found that the Garmin Nuvi 350 I got was cheaper on line than in Wal Mart's store as they are trying to build up their online store. Free S&H to the store just go there and pick it up. Nice option if Wal Mart is clsoe enough to home.
Pretty good deal I have one in all of my vehicles now, much easier than trying to lend one out to the wife and kids.
As long as it announces the street/road you need to turn on I am fine.
The higher end versions put MP players and other frill I don't need but maybe some folks do want (again, all my vehicles have XM radio so I don't need the MP3 deal in GPS).
Then there is the size of screen deal. Bigger is nicer but I can deal fine with my NUVI 350.
So, check them all out and see what you really want vs. some of the extraneous stuff they add on to increase the price.