Rinoa is very useful because of Angelo, who will randomly come revive characters, or heal characters; this is something you don't get with any other character. (note that she has the second highest amount of weapon upgrades)

Selphie has her special magic (Full Cure, Wall, Rapture, The End) some of which is so powerful that some will consider it cheating, as The End will kill almost anything, including most bosses, in one cast (instantly).
Also, she can hit Cactuars without needing to juction to hit% (with Strange Vision)

Quistis stands out because of her Blue Magic which can do anything, other than kill 'harder' bosses instantly; her Shockwave Pulsar can do up to around 30 000 damage (breaking damage limit)

The rest are damage dealers, of which squall can use the trigger, and has the stronger weapons/limit breaks.


Junctioning tips: 100 ultimas, full lifes, lifes, and shells make you absorb 90% of elemental damage.
also use the bonus abilities and PLAY CARDS (you can get the punishment before Ifrit this way, also you can have magic like tornado, blizaga, at that point just from cards)

About the XATM-092:
You can learn Siren's Mag-bonus ability dight after getting her, just make sure you can do about 4-5000 damage in about 30 seconds, and you'll easilly be able to "defeat" the robot, get it into reparing mode, run away, repeat; the more you can do this within 27 minutes or so (you'll the rest to get back to the ship) the more AP you get (50 each time)

And when you're far enough, yes Devour everything that does NOT kill/hurt you when you do so.

Have fun with this, it takes time (10 hours of playing cards is decent before the fire cavern)
You know how to get LionHeart before galbadia garden? It's time consuming and you have to level a bit early on.