Do which ever you like most first. Both are incredibly hard to 3HC unless you have some damage control in the form of Protection Ring, but note you should only ever use that when going against the later bosses, not against regular enemies. I recommend the Red Ring as well, if you can manage. I don't personally remember 3HCing either game simply because both are incredibly hard to play (I can play OoS without any trouble without restrictions, OoA eats my mind away though), but I'm sure with the trouble I had playing without restrictions, I'd pretty much be on a tight leash if playing 3HC.
If you play OoS, I recommend Prot Ring when fighting any boss from Dungeon 5 onwards. I've never obtained that Blue Ring, but I hear it gives you (2x?) Defense at no repercussion to your attack rating, so that will be a plus if Prot causes more damage than having double defense. I would generally have Red Ring, Blue Ring, and Prot Ring as the 3 rings always in the box, but that is just me. Take it slow and steady and try not to ragequit!