I think this is a very personal decision.
I bought a black one because I thought the white one looked a bit cheap! LOL! I think the black one looks much classier - so we are all different. I also found the blue button to be distracting. On the black model the button is a much more subtle grey.
Also (and probably more importantly) I think the contrast of the page was better with the black one. For me the page looked whiter which in turn made the print look darker. Of course this is an optical illusion as the actual page and print colour don't change just the border of the Kobo around it.
You should look at both yourself and make your own decision - there is no right or wrong answer for everybody.
