PS: The comparition is not made by me. I just repost the info here to help those who are interested in Priest/Mystic. Hope it will be helpful to some of you.
---Several buffs which last 10 to 25minutes. (Attack, Run Speed, Defense, Resistance, HP Regen.)
---Absorption Shield (absorbs around 10k DMG at LV58, is cast on your entire party)
---Ability to kite if needed
---Dodge also slows Movement speed in a small aoe centered on you.
---Dependable self heals
---Easier to heal with.
---Can "cure" knockdowns
---Their sleep is only one target.
---Can only give mp to party with use of a glyph at 58.
---They don't have any spells that effect their party's criticals/reception of criticals.
---Fiery Escape can put you in combat
---Lock-on Heal has a HoT
---Auras (Crit rate Or Run speed) and (Crit Resist Or MP)
---Orbs Can be laid ahead of time, Orbs also act as a "cure over time"
---Better kiter due to DOT being castable on the run
---Teleport skill with a glyph that has a 25% chance to reset the cooldown. Extremely useful escape.
---More mobility than priest
---Can give their party mana back with orbs, Aura and an attack.
---Has a self-resurrect skill that can be cast on party members and glyphed to apply to Self.
---Healing Fairy is OP, can restore you to full hp in moments. also cures on every heal it casts.
---Can sleep 2 targets
---Has multiple aoe CC skills (stun/fear etc) (all but the stun can be cast on the run)
---Ability to lock down bosses with chain CC (once their full arsenal is available)
---Usefulness of Tank/DPS pets are debatable bordering on useless
(tank pet really only useful for soloing BAM's)
---Cant force people to pick up orbs
---Has to depend on Fairy or orbs for self heals
---Orbs and Fairy do not benefit from weapons heal boost.
---Can only have 1 pet out at a time
: Future patch will give Mystics a Party Shield and Priests a self rezz, Exact details not known.
Overview of Healing Differences
The "main heal" for both classes is the lock on heal, both are about the same in heal power. Which is why both classes can heal all the content the same, the big difference is that the Priest has aoe heals on top of this and an aoe hot they can throw. It is possible for a priest to heal without using their lock on heal by relying on their aoe heals. The other big catch is that the mystic fairy and orb do not benefit from the heal boost on their weapon only their lock on heal does. All priest heals benefit from the weapons heal boost (including the 1.8% HOT).
Priests are the "Safer" healers, where Mystics have "enough" healing, you will have a much easier time keeping a group up as a Priest, the big catch of course is that mystics CAN heal a group through all the content a priest can. In a way Mystics give up the "safety net" heals of a Priest to gain powerful CC abilities and some nice buffs.
In my opinion, the Priest is a more defense healer built to handle the [filtered] hitting the fan with heals and shields, where Mystics are a more offensive healer that will dip into their CC abilities to Keep their party up when all hell breaks lose.
Special Note from Eziel's Lancer Guide:
I am posting this quote here for visibility as i think it will help out future healers and I am aware not all healers spend the time reading up on the tank guides, Note this is specific to a Lancer Tank:
"If you're a Mystic or Priest, please do not heal a lancer immediately when health drops. You will pull aggro very quickly this way if you are healing the lancer every time we drop 5-10% health. We have Second Wind which heals 14.3% of our life roughly (at level 22). I’m not sure what the norm should be, but my preference would be below 50% life." -Eziel
I Realize not all healers will be comfortable or have the confidence to follow this advice so I would also like to add that you should probably inform your lancer before you do this and make sure they are on board. It should also be noted that you will generate less aggro if you mix in attacks and do not just sit back and heal.
Base Stat Comparison
(Note Information Reflects KTera Until the next CBT)
Priests Have Slightly more HP and Resistance
Mystics Have Slightly more Endurance, Balance, Crit Rate and Crit Resist.
KTera Screens showing this compare
Proof that Base stats do not increase as Characters Level
1) Some skills have multiple components and therefore fit under multiple categories. To avoid confusion by posting a skill description multiple times and possibly giving the impression that a class has more skills than they do, the description is only in the section that coincides with the skill's main function. For example, a buff skill may do minor damage, and so while it's description is in the buff section it will also be noted in the damage section. The noted areas should point you to the section where the original description is.
2) There are certain glyphs that add extra utility to skills. As these can add possible customization and utility to the classes, these glyphs are also listed. Note that it's unlikely you will be able to use all of these glyphs at once. Do not assume your character will have all of this added utility, only that it's possible to attain.
3) Each description uses the raw numbers of the skill's highest upgraded level.
4) These are the Korean Tera's version of the skills. It's not yet known if NA will use these same skills and numbers, or if modifications will be made. Take this with a grain of salt.
Comparition between Priest and Mystic
Source from: TERA official forum