I have both a Garmin Legend and a Magellan Platinum. The long and short of things are the Magellan is a better GPS.
It has the ability to take SD cards to store maps. Right not I have a 128 mb card in it for maps. I have all the states on that I visit and hike in(Pa, Ny, Va, MD, DC, NM, and many parts of Ontario). The Garmin can only take 8mb of maps. I cant even put the whole sate of Pennsylvania in it.
In my expreience the Magellan has a better antenna. It locks on to sattalites faster and maintains lock when in wooded areas. The Garmin's reception gets spotty when under cover. For an example, my Magellan will get lock in my house. The Garmin will not.
I will not completely bash Garmin because it's a small GPS and not as bulky when I'm backpacking. I don't feel uncomfortable with the Garmin, but the Magellan has the Garmin beat hands down with the ability to take SD cards. To my knowledge Garmin doesn't have any intention on making a GPS that has the ability to take cards. One thing about being a small GPS though....the screen is harder to see while moving.