RSA VS INDIA IMO. Let's assume that both teams played a 3 tests series home/away vs the other teams here's my opinion as of right now:
India would completely smash all the other teams at home and possibly win by atleast 2-0 versus any of the other test sides at home.
Away, they'd beat WI, win or draw in SL and either lose or draw in the UAE vs Pakistan. They'd get smashed in Australia,England, and lose (not get smashed) in Nz and RSA. They'd win in both Bangladesh and Zim fairly easily.
At home RSA would smash by atleast 2-0 the following teams: WI, SL, PAK, ZIM, BANG, NZ. They'd either draw or lose to England and Oz. They'd beat India at home but not crush em.
Away RSA would probably win in NZ, WI,BANG, ZIM rather easily. They'd get smashed in India. Win or at the very least draw in Oz and England. Versus PAK in the UAE, they'd either lose or draw and win/lose/draw in SL.
Overall, I feel RSA and India is too close to call. I give neither team a chance of beating the other away. India would probably be more competitive in RSA than vice versa. India are dominant (scarily so) at home and okayish away. RSA are very good but not dominant home and away. Only place they'd be rolled is in India. Still I'm undecided.