White Mage, Scholar, Astrologian PROS and CONS
Easiest healer to pick up and play
Biggest heals in the game.
Best AoE heal range.
Best overall Heal Over Time (regen, medica 2, place-able aoe heal at like 54 or 56)
Stoneskin (a handy ability for any healing role and paladin)
Best burst damage of any healer, especially in large groups of enemies (Holy is amazing).
WHM's base class Conjurer is literally the only healing class (the rest are jobs: SCH unlocks at 30, AST gated behind HW expansion). Can get used to the role from the start.
CONS: Stoneskin is only shield, only useful when used outside of battle (less efficient to use in battle unless prepping for a tank buster)
Stoneskin 2 is just AoE stoneskin and can not be used in battle
Tetragrammaton (only instant heal) is on a 60 second cooldown
May have some MP management issues if using the given abilities at bad times.
Outside of HoTs and Stoneskin, WHM does not have many buffs for party members.
Some find WHM boring, feels less active than SCH and AST in regards to ability use (cures, aeros, and stones are mainly what you'll be hurling)
Adloquium is arguably the best shield ability in the game (the ability heals and places a shield, if crit it heals for the amount shown and doubles that amount for the shield placed. ex: adlo for 500 is 500 heals + 500 shield. Crit for 1000 is 1000 heals and 2000 shields)
Has an ability to add %10 damage reduction (I think, might be +10 defense/mdef) in an AoE
Best overall damage output of any healer
The Fairies Selene and Eos are constant cure bots with abilities to help you heal or help your party do more damage, among a couple other things
Good MP management with Aetherflow and Energy drain
Good party buffs through Selene
Only heal over time ability is Selene's Whispering Dawn
Shields are Scholar's primary concern, burst healing is difficult to do without saved Aetherflow stacks for Lustrate (I'm not familiar with the post 50 abilites, so I'll not comment on those)
Micromanaging your fairy is a must in difficult fights. That means placement and controlling when their abilities are used.
Arguably the hardest healer to learn to play at a high level (i.e. in hardest content).
High Crit is a must, big shields are dependent on crits.
SCH's AoE heal applies shields, but does not double the shield with a critical, unlike Adlo.
Has 2 stances, Diurnal and Nocturnal. Each changing the properties of the Aspected Benefic and Aspected Helios spells (adds heal over time and shield effects, respectively)
Can fill in for White Mage or Scholar because of stances.
Great utility through card mechanics
Cards can buff attack, attack speed, defense, lower cooldown times, refresh MP, and regain TP.
Cards can be stored for later use, and cards can be use to enhance the next drawn card.
Aspected Benefic is an instant heal upon use, Diurnal Sect placing a heal over time and Nocturnal Sect placing a shield equal to the amount healed + 33% iirc.
The Regen effect from Diurnal Aspected Benefic/Helios stacks with Regen/Medica 2 from White Mage
Can use Lightspeed for hastened cast spells over the course of a few seconds (allows you to move and cure while running).
Has an ability you can place on another player, it increases the amount of HP healed on that player when healing them, and if you heal another player while it's up, half of what you healed is applied to the target of that ability.
Best looking Limit Break 3 of any healer, arguably of any job.
Can boost the duration of ALL buffs you applied to a target by a fairly significant margin.
Collective unconsciousness is both a damage reduction AND heal over time field of effect
Can NOT switch between Diurnal and Nocturnal sects in battle. Once the battle starts you are locked in.
Cards are random and is VERY HIT AND MISS trying to get the cards you want or need.
Overall healing performance is lower than either White Mage or Scholar
Overall damage output is lower than the other two healers
Scholar shields overwrite Nocturnal Sect shields, and vice versa. (with a scholar you essentially must be in diurnal)
Does not gain Eye for an Eye or Virus as AST's cross class abilities are from Conjurer and Thaumaturge.
Collective Unconsciousness restricts your movement, if you move the ability ends (whm and sch can place theirs and forget about it)