I have just updated my whole set of front bulbs (minus the indicators) with Osram Cool Blue Intense (4200k).
The H7 and W5W's look loads better at night, they give off a really nice white light and provide really improved visibility from the standard bulbs. The H15 Osram Cool Blue Intense (3700k) let me down a bit as this still looks quite yellow in the daytime.
I would definitely recommend the H7 and W5W. In order to complete the set I changed H15 as well, although this bulb is pretty expensive at the moment and doesn't give the white light in the day that i would have liked (although i didn't expect that much).