The Garmin handhelds mentioned are all good. The Delormes are ok but the earlier models were known to be slow. Magellan hs the shittiest customer service. Avoid. Garmin's is spectacular.
I use a Garmin Nuvi 550 (dashmount) with the Midwest topos loaded via an SD card too. I can use t as a handheld for a couple hours if I want too.