Rikku in X

[Jessweeee♪]

And you want to customize your weapons.

[Depression Moon]

Rikku is mad useful in this. She can instant kill non-boss machine-type monsters. Her bombs hit all enemies at a time, she's quick, she's the only one that can steal from in game treasure chests, al bhed potions are really useful for most of the game, and her overdrive if you know how to use it correctly is some powerful stuff!

[Jinx]

And you want to customize your weapons.

The game is pretty much impossible if you don't.

[Cloudane]

I'm with the consensus - ignored her during the first playthrough, but found her to be a good "advanced player" character when I'm more knowledgable and stealing things for upgrades, sending her onto Auron's grid, dismantling the abundant numbers of machina enemies etc.

Some say she can even vanquish an Ursa Major

[Formalhaut]

If you took Kimahri down Rikku's path, and took him far enough to get Steal and Use, certainly, there's an argument there that Rikku's initial advantages (Stealing and using) have been overtaken by Kimahri. However, her real strength is, as a matter of fact, her surprisingly high HP and strength values. Her first "circle" of nodes boasts many nice HP boosts, and she does get a fair amount of strength, given her appearance.

Actually, if anything, Yuna was the character I really struggled using until endgame. I didn't really need to heal much. Speaking of her, I hardly ever used Aeons either.