I'm going to build Sakura and I was wondering which one is better for her. I can use a +Res or a +Atk.
All i can have access are:
Kumade + (Also can give her wrathful staff if needed instead of Kumade +)
I'm not the expert on this, but Pain+ is for a more offensive build (you can use if you want the +Atk), and use it with Savage Blow 6. You can also use Fear+ for good support utility, since she heavily debuffs the foes' attack. Gravity is also good support utility. Absorb is not that great, and I don't know about Kumade. It really depends. This is what I think:
Support: Fear+ (good and also budget)
Sakura is a pretty balanced healer, so you can build her either way. However, her effectiveness and your choice of IV is going to depend more on the team you build her with and how you will use her with the rest of your team. Unless you plan to use Sakura to tank mages, you will want a +ATK. It gives you a more flexible build and is generally more useful in arena where you see more melee than ranged.
Generally, you should only look at Pain+ for chip damage, and it works especially well if you have a vantage-hp tank (high HP and high damage characters, like Karla or Bartre, who take a hit to drop below 50% hp and then use vantage to kill everything that attacks them).
Absorb+ is better on healers with a higher attack stat (like Genny or W!Eirika).
Gravity+ is also a viable tactic but generally more useful on flying or cavalry healers who have the mobility you can use to exploit for kiting.
The others: Fear, Panic, Slow, Kumade are all situational and their usefulness will depend greatly on the map and enemy composition.