One Day...
AH elite
100% agreed BruceYebbo, but they are not as easy to hunt as the other species mentioned.

Actually I am not really sure how the "list" came together but it surprised me a bit, and to this point I am not really sure which one dmyers intended to list (Reedbuck or Rhebuck).
In the 4 criteria proposed: "1) Not common to see good one 2) hard to hunt specially 3) unlikely to see on future safaris due to their range and 4) Just really interesting cool trophy to take," to me the first 3 are fairly objective and the 4th is highly subjective, so I would take it out.
If so, my ranking would be
1- Vaal Rhebuck by a wide margin (not common, hard to hunt, very limited range)
2- Mountain Reedbuck (about halfway in the 3 criteria between Vaali and the rest)
3- Common Duiker/Steenbok/Impala/Blesbuck/Warthog. They are not hard to hunt and they are plentiful, even though like for everything you can't shoot one that you do not encounter and some folks indeed may spend a week in Africa without bumping into a decent warthog.