Related
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.
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 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 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.
Bonus Type
Augmented Healing