wich sonya is better?

I'd say +res -def is better overall, as it helps her maintain her role as a magic check, but +attack -res is still pretty good, particularly for offense

I would say +Res/-Def...defense is her best bane and +Res makes her a solid magical tank. Her attack will still be decent and her tome gives her the +10 to specials as well.

I have a +res/- hp and just merged a +atk/- hp copy into the +res one.
Personally, I think +res is her best boon because she has enough offense with Dark Excalibur.
Also, she's a debuff machine with res ploy natural to her and the atk ploy seal we got from the last TT. The higher the res, the more often it'll proc.