Only sane choice for new movies is an old republic movie.
The strory between the trilogys is too boring for not-star-wars fans, after ROTJ is stupid because the actors are too old.
While I'd prefer the new movies to be set in the old republic, I can't see it happening. They probably won't want to introduce a completely new set of characters to audiences that are only familiar with the films (not the EU). My money would be on post-ROTJ with Luke/Leia/Han appearing in a more minor role, potentially with their children/grandchildren as the protagonists.
They won't want to be seen to deviate too far from the original films - starting again in a different time with a completely new cast and characters will be taken poorly by lots of casual viewers.