I think that for each variation of treatments and finishes they do, the white models tend to look dated the quickest. But I'm a case guy, and I like black carbon cases, so the contrast between white phones and carbon cases is too stark.
If you are just putting it in a case, white will more visibly show the accumulated grime. But the color doesn't matter as much in that scenario anyway.
I've always preferred clear cases, and I notice when I get the white iPhone it definitely stays cooler (especially when used as navigation in the car).