I am a surveyor and use GPS' daily in my work. The Garmin line of GPS' are the most user friendly of them all, I think. They are also among the most durable. I have used several of the E-Trex models and they are really good, as well as being very compact. Better to operate are the GPS 76 models, but any Garmin will do. The Lowrance units, while being very accurate, are harder to operate than Garmins. The Magellans are also accurate, but not very tough (buttons are known to rip off, for one thing). Any Garmin will do. If you just want some positioning info, and not necessarily a lot of maps and such, buy any cheap GPS, as they all work good. The elevation info on the summit works well. I believe it is a barometer which provides corrections to the elevation calculations in this unit, so you can get accurate RELATIVE elevations (relative to your last KNOWN elevation) this is dependant on barometric pressure. Hope this helps.
I ride with the Legend, works great. You can download your tracks to your p.c. and look at them on google earth in 3-D. Definetly get a mapping unit otherwise you just get numbers to look at. The topographical upgrade shows great detail and contours.