As I understand it, when using an adapter you cannot use PDAF in video mode with the A7RII.... so I guess, technically the A7SII will have better CDAF than the A7RII because of the number of points and the a7SII's better low-light allowing for focus in darker images.
I, personally, chose the A7SII (after owning the A7S) becuase I watned the shallow DoF of a full-frame sensor and didn't want the crop factor of S35/APSC. i guess you get used to using one type of tool and you don't want to change....