This question is invalid, as ionic bonds do not exist in physical reality. An ionic bond (defined as two or more ionic elements attracted by opposite polarization of said ions) would require near-infinite electronegative difference. Thus, all ionic bonds have at least some covalent instance. An example in my textbook gives the common salt Sodium Chloride (Na-Cl) as having a NEARLY pure ionic bonding, whereas Silicon Dioxide is generalized as an ionic bond but has nearly 50% covalency.
Tl;dr ionic is stronger.