On the new W-9 forms there is a specification for an S or C corporation, what is the difference and should they receive a 1099?

Corporations do NOT get 1099s under the old tax law, and, now that the new 1099 requirements have been formally revoked, they do not get 1099s under current law as well.

As for the differences between a C and S corporation, do a Google search on that. Whole books have been written on the subject.