I find that a GPS is most useful for keeping track of where I am (including direction of travel) and anticipating nearby travel choices. The small screen is not good for looking at the big picture. Yes it can give you a route all the way across the country, but it's a pain to review that route in detail.
When looking a GPS reviews, try to get a sense of what experience and expectations the review has. Ignore reviews from 1st time GPS buyers who don't have realistic expectations. You'll learn more about their ignorance than the unit.
MS Streets & Trips is a good planning tool, though not necessarily the best. A bit plus is that it is self contained. You don't need an internet connection to use it.
I prefer Google Maps. The amount of information about most roads is unsurpassed. I use 'terrain mode' and 'streetview' a lot.
Learn also to use various state DOT websites. They have webcams showing weather conditions, traffic reports for cities and major highways, and construction reports.
For camping information, I use state park websites, National Parks sites, and National Forest sites.
