Regina, I've done a little editing. Make sure you differentiate between the measurement of the elevation of a certain point on your route (i.,e., at the top of Mt Diablo it is X feet high) and the calculation of the total feet you've climbed (i.e, I just rode up Mt Diablo and climbed X feet total). These are two different things.

ForeRunner: GPS elevation only. Much variation/error on gain/loss calculations (only available once you've downloaded your data to the Training Center or MotionBased). Essentially worthless for elevation gain/loss readings but fairly accurate for measuring the elevation of a certain point.

Edge: GPS and barometric elevation readings and gain/loss calculations. Some variation/error. Generally more accurate than GPS alone. Not perfect, but okay for consumer grade.