I had the white 3GS. Never again. It always got dirty so had to be kept in a case, so you wouldn't be able to tell the difference anyway. The 4 is different with having the White front but IMO the black looks much better...
I went with the white one... I have it in the Incipio two-toned pink SILICRYLIC case and it's perfect!
Of course it all depends on your preference.