I'm guessing that when you say form, you mean shape. :think:
Anyway, they all are the same shape as the stock plastic. Both are good quality. I have not tried One industries, but I am sure that they make a good product also.
A friend of mine once told me that he didn't like Acerbis plastic as much as UFO because the edges were sharper. He noticed this when lifting the bike by the rear fender. Personally, I haven't noticed this but maybe others will agree.
I don't think you can go wrong with one of those 3 companies.
I have heard that Maier plastic uses a different process and doesn't look, fit or last as well as the big names.