Hoya filter lineup question

many have asked whether a filter is necessary - but moving that question aside, i'd just like to know what is the best filter (and best Hoya filter) by understanding a bit more of their lineup.. can anyone help?

There's the Hoya 'standard' ones which start with:
1. bare standard
2. HMC (96% light transparency)
3. super-HMC (99%+ light transparency)
4. Ultra
with prices increasing in that order..

But then Hoya also has Pro-1 D for digital cameras.. what's the difference between a Pro-1D and an HMC or super-HMC? anyone knows? and what is the light transparency for Pro-1 D?

And other than Hoya, is B+W meant to be better (in the sense that it affects image quality least/or improves it most)?

Also, how do Sigma filters fare against Hoya? the salesperson suggested Sigma over the Pro-1D

Basically this thread is about the best choice if you had to put a UV filter on a lens. Thanks!