I have 17" VW Motorsport alloys in anthracite on my Polo GTI and really like them; the design makes them very easy to clean, and being powder coated, the finish is much more durable than a diamond cut lacquered finish. I got mine from VW Motorparts at the first link in your post, and the service was excellent; very prompt response to questions I e-mailed to them and next day courier delivery.
For the Polo, the current colour options are either Black or White. Anthracite used to be an option for the 6r / 6c Polo, but VW now only have the anthracite option as a 19" wheel with a bolt fitment of 5x112 (the 6r / 6c Polo wheel bolt fitment is 5x100).
Whether or not white would look better than black I think depends on what colour your car is. IMO white wheels would look better on a darker coloured car and black on a lighter coloured car. Also, if you do decide on the white Motorsports, dirt and brake dust deposits will be very noticeable, so you'll need to be prepared to wash them very frequently to keep them looking good.
Really pleased with mine. They don't require any special maintenance; they get cleaned when I wash my car (the front face with a Wo-Wo microfibre wheel mitt, and I can get my Wheel Woolies between the spokes to wash the backs). A couple of coats of wax or sealant twice a year keep them looking like new.
