I don't think anyone really knows yet. I'm assuming you're referring to 7th, 5th, and 9th?
2nd brings a fair amount of damage to the table but 8th brings armor shred. It's a tough call. We'll find out in two days, I guess. They're all needed for platoons eventually though so you may as well take them all to R7.
F2P since the last time I bought Kyros, Crystals, or the Conquest Pass.
Xaereth recently did a video on relic order for them. Obviously you will need Grand, but my advice would be to hoard until others do the mission and post videos on it then relic and mod accordingly.
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2nd brings a fair amount of damage to the table but 8th brings armor shred. It's a tough call. We'll find out in two days, I guess. They're all needed for platoons eventually though so you may as well take them all to R7.