Weapon Enhance for W.Chrom

go for Def, atk is almost never worth it, and you are already +Res (Also there is NO reason to go for speed) so going for Def will allow him to take more hits, and give him more bonfire/ignis damage

I say go for res. 35 def and 36 res is no joke on a green unit with Wary Fighter

I have +res -hp, I ran a bunch duel simulations and it seems like the def upgrade gives him the most benefit, so that's what I went for. I was deciding between res and def too, and I don't regret the decision so far. It's pretty great.

Go for +def, since you're not running DC, that means he'll mostly be dueling physical units (his natural resist and wary fighter should allow him to survive most magic match ups anyway).