Bob, what Im specifically looking for is a unit that I can put on the dash for road trips to unknown areas.
If you already have a laptop, then it's hard to beat either Delorme Streets Atlas or Microsoft Streets & Trips. I've been using Delorme for over 10 years now.
My job has me travelling all over the country most of the time. Sometimes I drive, but mostly I fly in and pick up a rental car. With the laptop, I can figure out where my work sites, hotels, etc. are and mark them on the map. When I arrive in the area, its as simple as picking my starting and finishing points.
Both programs will give you spoken turn-by-turn directions as you drive. Delorme also has voice input so you can control most of the major functions without taking your hands or eyes off the road. Beyond that, it's really a matter of preference. The two programs have wildly different interfaces, so most people tend to love one of them and hate the other. No map in the world is 100% accurate, so you will sometimes bump into those errors.
One thing is the price. If you already have a laptop, you can get the software with GPS receiver for $100 - $150. Throw in a DC-AC inverter to keep the laptop running, and you have a Cadillac system for just a little money.
If you don't already have a laptop, then you'll probably want to look at one of the small units that stick to the windshield. Some of them look pretty nice, but the laptop screen has me spoiled. I don't think I could go backwards.
Be aware, the laptop with wires & such can get pretty fiddly. Most of my travel is by myself. In that case, I put the laptop in the passenger seat and life is easy. When I travel with the family, it has to sit on the center armrest and one of us has to hold it. If my 8-year-old grandson is along, he loves to hold it in his lap and operate the computer as we go.
I could invest in a Jotto Desk or some other laptop mount in the truck, but I just don't use it there often enough to justify the cost.
Hope this helps you a little.
Bob