I reckon that in the long term, Santon will be our starting RB (remember that he's still only 20 and he's already comfortable playing on either side).
But as it stands, in the short and medium term (as in the rest of the season and possibly most of next season), he'll be our starting LB imo.
I have no problems where he starts really, be it at RB or LB, he'll be an asset to the side.