My choices:
D) continue where Crisis On Infinite Earths left off
Or actually, after 1988/1989.
Pull a JJ Abrams and just go in a different direction from that point on.
This would be the easiest route, and with trade paperbscks of the Levitz run available, it would also be accessible to new readers.
Why 1988/1989?
Simply because DC could release the Who's Who in the Legion of Super-Heroes, along with the Secret Origins issue that came out the same time, in a nice single trade paperback.
Almost all of the major Legion characters are from before that time, as well as all the major storylines and history.
F) pick up right where Paul Levitz's most current Legion left off
This one would work, too, as originally this was similar to D, above. The cut-off point was the end of Magic Wars, which still included the majority of Legion's history.