I think it depends on how high you need it to grow, I have 2 buddlias, but not a lot of people like them but i find them to be very fast gowing and attract butterflies, if you dont let them get out of hand they can be quite attractive, or you could go for a lilac bush they provided a nice scent, and come in white or purple, the davida is the ones i chose.

Sounds like you need something evergreen rather than Buddleia, which isn't - you'll be in your lounge in winter with the lights on, so an evergreen would be better, I think. None are particularly fast growing (except for Leylandii cypress) and the trouble with fastgrowing plants is they get absolutely enormous. If you're desperate for cover, how about erecting a trellis for instant cover and then growing an evergreen climber up it, something like Trachleospermum jasminoides, if the position is not to exposed to cold northerly or easterly winds, and there's sun. Otherwise, Escallonia or Euonymus pictata, Berberis darwinii, Pyracantha.