Help me decide which Brave Ike to use and merge upon

I'd use +HP -SPD, - spd is kind of beneficial if you use steady breath since it ensures ranged units will double him which is good because they wont really do any extra damage and it will lower his special by 2 allowing him to use aether the next round, +HP will help him be a bit more tanky to magic and physical which is nice, Ike can run a lot of different ivs fortunately
Or if you're using distant counter the +spd might be better if you can pair him up with brave lucina to raise his speed to 37, then use quick riposte and he'll take out a lot of units :3
He's great either way so pick what you prefer (except -Atk, you're right that sucks xD )

Well its a hard choice tbh. It basically comes down to how do u want to tank better. By having a little more spd to try to avoid follow ups. Or having a bigger hp pool to tank brave users since its unlikely that that it will matter much.
Imo id say go for the hp one. Most of the time ull get doubled anyways and itll serve better to tank hits anyways.

I also think u should reserve one for skill inheritance. Steady breath looks hella fine on a tank like xander

Well its a hard choice tbh. It basically comes down to how do u want to tank better. By having a little more spd to try to avoid follow ups. Or having a bigger hp pool to tank brave users since its unlikely that that it will matter much.
Imo id say go for the hp one. Most of the time ull get doubled anyways and itll serve better to tank hits anyways.

I also think u should reserve one for skill inheritance. Steady breath looks hella fine on a tank like xander