What is the equation for the acid ionization constant of HF?

HF(aq) ⇌ H⁺(aq) + F⁻(aq) …… Ionization constant, Kc = [H⁺(aq)] [F⁻(aq)] / [HF(aq)]

OR :
HF(aq) + H₂O(l) ⇌ H₃O⁺(aq) + F⁻(aq) …… Ionization constant, Kc = [H₃O⁺(aq)] [F⁻(aq)] / [HF(aq)]

Ka = [H+][F-] / [HF]

ionization means HA=H+ + A- (not the reverse). the equilibrium constant is K = Products over reactants, in this case (H+)*(A-)/(HA)