I am still using my old, clunky Magellan 315. I have used some really tricked-out, more "modern", GPS units, but I still prefer the old monochrome beasty. I really like the interface and the menu layout, and the ease of inputting a projected waypoint.
I ALWAYS carry a paper topo map (usually a waterproof paper map with UTM grids) and compass, and use the GPS only as an additional navigational tool. I prefer large maps so I can view my position in the context of the larger detailed landscape, something that can't effectively be done with a small screen. I use UTM, and, again, I can do that with either the paper map or the GPS unit.
To me, the value of a GPS receiver is to easily find my position so I can verify it on my paper map, especially in terrain with few navigational landmarks or adverse conditions (e.g. heavy forest cover, swamp, nighttime, heavy snow, etc.) I don't need lots of bells and whistles to do that. My ideal GPS receiver would be cheap, very lightweight, very small size, miserly with battery consumption, have both lat/lon and UTM coordinates, be able to use at least WGS 84 and NAD 27 datums, store a few waypoints, project coordinates into waypoints, and mark locations as saved waypoints. I don't need color screens, map displays, or any of the other myriad "enhancements" that seem so prevalent. My old 315 meets most of those requirements, with the exception of size and weight.
My $0.02. I would welcome comments, observations, opposing viewpoints....