The correct order of increasing covalent character of silver halides is

The cation is fixed, so anion polarisability controls the trend. It increases with anion size: $\mathrm{F}{}^{-}<\mathrm{Cl}{}^{-}<\mathrm{Br}{}^{-}<\mathrm{I}{}^{-}$. Therefore covalent character increases from $\mathrm{AgF}$ to $\mathrm{AgI}$.