I like the Space Gray, but I am too ocd about scuffs and scratches to deal with seeing silver aluminum beneath when it does, so I am stuck with white and silver, and will be for the foreseeable future. I wish they offered a black bezel with the silver body like all previous iPads to the Air featured. Oh well. And gold? Never.
Color will probably be the last thing I will think about when buying future iPads. My choice of white for iPads this time around was due simply due to build issues (speakers, wifi etc. - every slate gray I tried to buy had issues. The silver/white did not.)
Now by the time I'm ready to upgrade again if they have anything that looks like that red Mac Pro as far as color... ask me this question again.
Probably black. I like how the bezels sort of disappear into the content when watching a movie or when reading a book with a black background. White content never really blends in with the white, on the other hand, because the whites are never the same.