Pixel Format Settings - which to use?

So I've read a few posts, and the help file, but let's capture this as something that is searchable in the future.

What is the 'best' setting in today's Quad Core and better world, to set HD projects at?

I've been defaulting to 8 bit, but should we be pushing to 32 (I assume so, as I'm running a 64 bit machine!).

And what about Video levels or full range? Which one when? Why?

Thanks in advance.

Alf