More stable among the following is
 

In general fluorides are unstable in the lower oxidation state. because the size of Fluoride ion is small in comparison to size of metals. Thus, due to size incompatibility, the bond is weak.

The ability of fluorine to stabilise the highest oxidation state is due to either higher lattice energy as in the case of CoF₃, or higher bond enthalpy for the higher covalent compounds, e.g., VF₅ and CrF₆.