In order :
Cynthia vs. Hunter J (possible, and one of these battles where I might die of coolness and beauty induced nosebleeding)
Cynthia vs. Cyrus (also possible, if the writers have enough brain substance to handle this evil team better than the last one >>;;; And, if they want to make it even better, torn world, plz. =3)
Cynthia vs. Ash (also possible with all the foreshadowing, but please, please, have Ash lose. >>)
Heck, Cynthia vs. anyone. XD! Just have her win. XD!!!
Not so possible battles:
Cynthia vs. Hunter J vs. Sabrina (*fangirlish squeal* Would so be the death of mine =3 But a good death)
Will vs. Sabrina (in a friendly way plz. =3)
Will vs. anyone (please, please, just make him appear already. >.< Agatha got an episode years after her introduction. >> Dito with Wallace.)