I've tried a variety of mounts, and I find that the RAM system is simply the toughest, holds things the steadiest, and is easiest to adjust. Expensive, but worth it.
I've had the Delorme Earthmate PN-40 since April of 2009, and have used it off-road extensively. I liked it enough to buy a second one off of CraigsList a couple of years ago.
Mainly I bought the second one to get an updated copy of the maps, but also so that I would have a spare.
The first one very occasionally locks up and I have to pull the battery, but that doesn't happen often, and after a reset, it's good. The second one has been rock solid.
I don't think it's the best GPS out there, not by a long shot. But I like the way the charging kit hooks up without traditional USB plugs so it's waterproof, and it works well enough for how I use it.