I think Doanire beats all of them. In order of who gives Nonito the most trouble I'd go: 5. Arce-I think he's ready made for Donaire and gets starched early. 4. Nishioka- Gonna come forward more than Rigondeaux and Moreno - which will play into ND's hands and scores a mid-late rounds KO 3. Mares- See Nishioka, I believe Mares fairs slightly better due to his youth and athletism than Nishioka 2. Moreno- I believe he will last the distance and pinch a few rounds but won't take many risks 1. Rigondeaux- His style would be awkward for Donaire, I won't engage as much as Mares/ Arce but Donaire would win in a largely uneventful fight.
Mares has the best chin of the bunch & IMO is the only fighter of the above who can possiblly hurt Donaire. I say Abner.
If Nishioka can land his straight left hand often enough he can pull the upset. He's a good fighter but is getting old and just isn't on Donaire's level. I think he get stopped by Donaire. Mares doesn't hit that hard....and definitely not hard enough to hurt Donaire. Once he starts trading left hooks, Donaire puts him to sleep. Rigo has a shot if he can avoid getting hit on the jaw because we all know he's packing fine Cuban glass. Moreno is the most skilled fighter on this list imo. I think he loses on the cards vs Donaire though.
I think a perfectly conditioned and serious (no showboat or lunge for the KO) Donaire will stop all of these guys. However, since he does. I feel that among the list, it's Rigo who will be much harder to fight. Not because of how great Rigo is, but of how two counter puncher collide. Donaire would probably say to hell with it take the initiative and end up fighting sloppy.