Can I suggest that you seriously consider the metal brackets. I insisted on the Clarity braces which come with tooth coloured wires because I didn't want them to be obvious (and Invisalign couldn't guarantee a good result). However, 9 months in to treatment I have been fitted with a metal wire as the coated wasn't creating enough friction to move the teeth. It is, in all honesty, a much cleaner, neater look than the coated - plus they are a cheaper option :)
Just thought I'd offer an opinion as it is a subject which comes up regularly on the S&B board :)