Winter chrom, best refine on mixed team?

I have a winter chrom with the iv spread +atk-speed. Here is his build so far, trying to get a feel for which refine to use on his slaying axe (attack, defense or resistance)? He's used alongside winter emphraim, legendary azura and eliwood. With the legendary effect of azura and a res refine he would have good mixed bulk, though a defense refine is tempting to handle archers (good for azura). Thanks!