From the little of what i've seen, Ajax basically have two ways of attacking, 1) mainly attacking from the centre shooting inside or outside from distance, and 2) crosses and wing play. They attack with pace, and obviously Dolberg is their most dangerous threat, but the other players should not be taken lightly too. They seemingly don't play with some kind of strong target man (I may be wrong), so we don't need smalling that much. Jones is a better option here I think.
Ajax often passes around the penalty box to create chances, always aiming to players at the centre to shoot from inside or outside the box. Jones and Blind is a better options imo for wiping the floor, intercepting their passes, and they're a lot better dealing against 'lightweight' players who rely more on pace, movement and dribbles. Smalling is a better option against bulkier striker. Valencia and Darmian is important defensively to negate their wing plays.
Either,
Valencia---Jones---Blind---Darmian
Or,
Valencia---Jones---Smalling---Blind---Darmian