Which Chrom?

I summoned 2 Chrom's on the Falchion banner. I am ecstatic because I need Aether fodder. However, the second one is +Atk/-Res. I have a 4 star Chrom that is +Atk/-HP. Which bane do you recommend I keep? Should I fodder my 5 star Chrom to my arena core team or keep him and promote another Chrom as fodder (I have 4 4 Star Chrom's).