Itachi. We know that normal ninjutsu wouldnt work on the 3 raikage and neither will taijutsu because of his speed and physical strength, but genjutsu will and this is where itachi has the advantage.
I highly doubt the 3rd raikage knows about tsukuyomi, if he does look into itachi's eyes and itachi uses this, he would feel the full effects of it, just like kakashi did, and with this would be greatly exhausted, this then leaves him open to amaterasu, because if itachi used amaterasu from the start the raikage would dodge it and itachi wouldnt use such an attach from the start. Also after the raikage has been exhausted from the effects of tsukuyomu, itachi can either decided to seal him with the totsuka sword or use yasaka magatama or amaterasu.
Thats one way. Or itachi can desperse into a flock of crows (genjutsu) then make eye contact with raikage (similar to what he did to sasuke). Either way once tsukuyomu hits the raikage, it would be too exhausted to do much.
Itachi doesnt need to figure out that raikage defense because itachi's abilities are actually the most effective against the 3rd raikage.
Also if itachi does catch raikage with amatersu then its game over although it will take time before it kills the raikage. Im not saying amaterasu is powerful than wind rasengan because it is, but thats not why it will work on the 3rd raikage.
Amaterasu burns, till its target gets turned to ash. Raikage does have a huge chakra reserve and with this will be able to protect himelf in raiton armour, but his chakra wouldnt last forever and neither will his armour. Once his chakra runs out, his defence (raiton amour) wouldnt protect him from amaterasu anymore and this is when it will burn him to ash