Vanille – Medic Crystarium

Character Vanille
Role Medic
Vanille and Hope are the only Characters with access to every Medic Ability, and while Hope's magic stat is naturally higher, Vanille is plenty effective as a Medic as well. She and Hope are the only Characters who can use the amazing Curaja Ability, a vital healing spell in the endgame.
Compare Vanille – Medic Crystarium to other Crystariums

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Vanille

Eidolon Hecatoncheir (Chapter 11)
Base HP 350
Maximum HP 21,050
Base Strength 23
Maximum Strength 1,400
Base Magic 35
Maximum Magic 1,700
Starting Weapon Binding Rod
Primary Roles Ravager, Saboteur, Medic
Accessory Crystal Saboteur 5
Accessory Crystal Medic 8
Accessory Crystal Ravager 10
ATB Level Crystal Medic 8
Chapter 1

Fang – Medic Crystarium

Character Fang
Role Medic
Fang has access to the same Medic Abilities as Lightning, but because it's a secondary Role, she's even less useful as a Medic. By the time you are likely to learn these Abilities, the lack of a Curasa spell means Fang will be terrible at healing. Her only real advantage over any other Medic is that she gets Raise (which Sazh and Snow do not), but you're more likely to use Renew or a Phoenix Down late in the game anyway.

Hope – Medic Crystarium

Character Hope
Role Medic
Hope has access to every Medic Ability, which combined with his high Magic stat makes him the best Medic in the game. He is one of only two Characters (along with Vanille) with access to Curaja, a vital Ability when dealing with powerful multi-target attacks from the game's tougher foes.

Lightning – Medic Crystarium

Character Lightning
Role Medic
For most of the game, Lightning is an effective Medic, if not quite on par with Vanille and Hope. As the game wears on, she becomes better as a secondary Medic, and by the time you're mastering multiple Crystarium Roles, she's all but worthless. This is entirely due to her lack of access to the Curasa Ability (to say nothing of Curaja). Cure just won't cut it once your party's HP is in the five-digit range, limiting Lightning's job as a Medic to casting Esuna and perhaps Raise.

Sazh – Medic Crystarium

Character Sazh
Role Medic
Sazh never gets access to Raise, but don't let that fool you into thinking he's a bad Medic. He doesn't get Curaja (that's reserved for Vanille and Hope), but he does get Curasa, making him an effective healer through endgame fights. That said, he won't get Curasa until Crystarium stage 9, and it's quite expensive.

Snow – Medic Crystarium

Character Snow
Role Medic
Snow has the same strengths and weaknesses as a Medic as Sazh—no Raise (which is no big deal) and eventual access to Curasa (which is very important when dealing with the most dangerous enemies). If you're actually going to use the Salvation paradigm (MED/MED/MED), make sure you're Characters who can at least cast Curasa.

Vanille – Commando Crystarium

Character Vanille
Role Commando
Vanille is the most limited Commando in the game (and has the silliest Weapon), lacking both Launch and Blitz. She does get Blindside and Faultsiphon, auto Abilities that are easy to take advantage of. However, her Role should generally be limited to that of a secondary Commando. She's more useful for the Augmented Attack effect than actual Commando Abilities.

Vanille – Ravager Crystarium

Character Vanille
Role Ravager
Vanille is a good Ravager with a number of holes in her Ability list. Like Hope, she lacks any -strike Abilities, making her unable to damage enemies that are immune to Magic. She can still advance their chain bonus (and doesn't need to worry about strength!), but this can be a big problem against certain foes. She also lacks Aeroga, Thundaga, and Waterga, and doesn't get the Vigor Ability. None of this is crippling, but it does set Vanille firmly behind Hope as far as Ravagers go.

Vanille – Saboteur Crystarium

Character Vanille
Role Saboteur
Vanille is a very effective Saboteur with a variety of Abilities, though she is more concentrated on defense-lowering debuffs. She cannot inflict Slow, Curse, or Daze, and also lacks Fogga and Painga, but has single- and multi-target versions of every other Saboteur Ability. Beyond that, she has Death, a unique Ability that either just kills a target or deals a large amount of damage to them. Since very few non-boss enemies are actually immune to Death, you can get cheap, fast kills against a number of difficult foes (up to and including Adamantoises) with it.

Vanille – Sentinel Crystarium

Character Vanille
Role Sentinel
Vanille as a Sentinel? Surely not! And truth be told, she's not very good at it. She has Mediguard at least, but not much else, including Challenge. She does have more HP than Lightning or Hope, but both of them are evasion Sentinels anyway. Basically, you don't want Vanille to be your main Sentinel. She's fine in the Tortoise (SEN/SEN/SEN) paradigm, but not much else.

Vanille – Synergist Crystarium

Character Vanille
Role Synergist
Along with Fang, Vanille is one of two Characters that has access to Bravera, Faithra, Protectra, and Shellra, high-powered Abilities that have a short duration to balance their extra effectiveness. Unlike Fang, Vanille has a decent number of standard Synergist Abilities as well, including Veil, Vigilance, and the Bar-spells. She is the only Character in the game that doesn't get Haste, however, so she's not very effective as your only Synergist.

Medic

Bonus Type Augmented Healing

Medic

Abbreviation MED
Role Bonus Augmented Healing
Base Bonus (Self) Healing Bonus: +10%
Role Level I Bonus (Self) Healing Bonus: +20%
Role Level II Bonus (Self) Healing Bonus: +30%
Base Bonus (Allies) Healing Bonus: +5%
Role Level II Bonus (Allies) Healing Bonus: +8%
Role Accessory Healer's Emerald (Grants Healing Bonus: +5% to self)