Natural is more appealing. I don't condone tanning beds and spray tanning looks awful but a little color can look good on people (from the sun) although this should be done in moderation with sunblock. I'm pale and have seen it look good but too pale like whiter than a sheet of paper doesn't look the best. But anything from milky to ebony can look good.
I'm a hypochondriac about a lot of things so if I'm even out in the sun for 15-30 minutes I put sunblock on because I don't want to get cancer so I never get tan but it's better to be safe than sorry in my opinion.
I agree with IHateMeganFox : natural is best. I am naturally really pale, and I think it looks better on me than a tan. However, a friend of mine is from Martinique, and she has a lovely light-brown skin colour that suits her very well. She wouldn't look prettier with a pale skin. I find all complexions pretty as long as they are natural. As for which I find myself looking at more, it's not a matter of skin colour but a matter of face. A pretty face is pretty, regardless of skin colour :)