+res -hp, +res-def, or +atk -spd for owain?

Atk/Def Bond > DC imo

Second one shouldnt even be considered. I think your best one will be +Res-HP. It wont interfere with your ability to soak and speed matter more to him than attack due to his bond skills and special with wrath.

A defense bane is pretty bad, so don't even look at that one. Both +Res and +Atk are good. His speed isn't really that necessary unless you're trying to kill blue units, in which case you'll probably want more speed so you can double, meanwhile a res boon can help him tank dragons a bit better then he can without it.

After using my +HP/-Res Owain, however, I'm gonna vote for +Atk/-Spd. In my experience, his speed is just not really that important, again unless you're trying to kill blue units, and even then a lot of them only survive by the skin of their teeth, so an attack boon would've helped a lot in actually finishing them off. It's not really often that he gets killed by a dragon aside from H!Myrrh (she's armored so she's an exception) so a few points in resistance is not gonna help him too much.

Also, Distant Counter, in my opinion, is not a good skill for him to have. Even with a res boon, he'll be taking a LOT of damage. Bond skills are arguably his best friend due to him wanting to stay near his allies anyway to have maximum damage from Blue Flame.