An article on a well known big USA forum recently covered the magellan explorist trx7 which seems a good though expensive all in one box of tricks for the USA.
Previously I've stuck with various Garmins, although I've just bought a second hand Panasonic Toughbook, and hope to stick some maps on from here http://www.quovadis-gps.de/online-shop
It seems you have to pay up for their software first, giving "normal" navigation, then you can use that to add in actual maps that have been scanned in, like the Russian military maps that cover lots of interesting places that Garmin etc have yet to get to. That gives you your position on a screen showing accurately contoured mapping, even if the road size and infrastructure is way out of date. Big obvious stuff like that can be had on a normal paper map for most places though I would think?
Interesting info on the Russian map sets here https://www.wired.com/2015/07/secret-cold-war-maps/
Sorry if getting a bit off topic
