i go for BLACK.
my reason is
3GS has heat problem, if u do wrong setting for push mail or push notification, ur phone will heat up and battery drain really fast(half day gone to 20% warning)
some ppl even notice slight discolouration on their white.
i already booked a white one, but the collection day itself i change to black, after i got the black i got no regret, bcoz the simcard slot will not show any black/dirty line..... and it will not become yellowish.
so which color would u choose?