Depends. Chulainn's guaranteed triple means she's capable of whipping out +90 burst in three turns - perfect for reaching a full burst ASAP. However, this has a long cooldown. Cybele is slower than that, but never ever slower than five turns for +100 burst.
So... if your aim is just one full burst, Chulainn first. If your build relies on chaingun bursts, Cybele first.You'll never want to use SRs and especially Rs in a "good" burst team...
Wind Rami Rami should be okay-ish if you have nothing better. But you should look to replace the R with literally any SR or higher, simply because of the damage difference. Titania would be ideal of course, if you're looking for burst generation.