I've never been comfortable on an elliptical machine. Occassionally I get sore feet from running on a treadmill, as I usually run on a gravel trail near home, but I really prefer them. Oddly enough, it still feels like I'm going somewhere with the treadmill, whereas I can't really translate the feel of an elliptical with any sort of accomplishment.
Like I said, though, I've never liked the feel of an elliptical machine, so my views are heavily biased
.
As others have said, find what you like more and stick with it - you'll be happier that way.
WarWagon's right, by the way, running is a lot harder on the frame. Just something else to keep in mind . . .