Women`s Flyweight. 105 and 145 have some notable fighters that casuals know (Waterson, or Cyborg), but neither division is half as deep as 125. The 125ers are quite established with some dominant veteran fighters (Porto, Maia, etc.), and champ (Barb Honchak) and a lot of new, up-n-coming talent (Bennet, KGB, Corso, etc.).
If you made me choose between 105 and 145, I`d go with 105 (AW) just because there is not as big of a talent discrepancy. Tiburcio can beat Waterson can beat Hamasaki can beat Brown can beat Tiburcio. Some of the smaller SWs in the UFC could also fight at their natural weight then, like Penne, Ham, Hill, and Ellis. And, there are some up-n-comers in this division as well (Yu Frey, Esquibel, etc.).
People who love Cyborg and want the UFC to make a 145 for her...I`m sorry, it`s just a terrible idea. There aren`t even 5 interesting fights you could make in that division. And the discrepancy in talent if too vast between the #1 ranked fighter and the #10 ranked fighter.
But, the worst possible choice for a new UFC division would be men`s super HW; I couldn`t imagine more boring fights. You`d either get a haymaker connecting and knocking out a guy in the first minute of the fight...or you`d get two huge fatties/roidies swinging wildly between huffing-and-puffing for 15 minutes. It'd be like playing Street Fighter II with 4 buttons that don`t work and an inability to pull back and block....ultimately, futile and tedious.
Jarl