As far as a preferred device, I'd just search for online reviews and see what features appeal to you best, etc. Do beware of GPS units that offer maps of the entire US built-in ... they deliver on the promise, but perhaps not at a resolution that you'll want to use on the trail. I think these are 1:100,000 or even 1:250,000, not sure. They want you to separately buy packages from them that contain 1:25,000 scale maps, so for that resolution (which is what I prefer to use), the true cost of getting maps from them is higher.
The whole thing can be reasonably simple depending on what approach you take, or it can be pretty complicated. On my smartphone I'm in the process now of trying to switch from National Geographic Topo software to using
www.memory-map.com software and free topo maps, but it's not totally simple, to include getting the overlay (plot, trace, whatever you want to call if) of any given trail (which is sort of what started this thread).
For most of the PCT, what I recommend is Halfmile's work, at
http://www.pctmap.net/. I believe he has all of California and a little of Oregon mapped now, and except insofar as the trail moves from when he mapped it (as is being done I guess in SoCal in a big way ...), this is really accurate stuff.
The other things I recently discovered is that if you can find a trail plot in a format your software doesn't use, the free GPS Babel software isn't too difficult to figure out to convert almost any format to almost any other. Wonderful.
http://www.gpsbabel.org/