I mainly do m+ but am looking to get into some PvP. I’d love to main a pure dps class but it’s such a pain to get into groups since I mainly pug. Fortunately, I enjoy healing. Thinking priest might be a good choice since shadow is pretty decent and there are two healin specs…
Thoughts?
are you looking to do RBG’s or Arenas?
I’d like to do arenas but imagine I’ll dabble in rbgs
not sure how priest is in arena in RBG’s Holy can be quite trouble some to deal with but judging from the last AWC i dont think priest is the most viable healer for arena’s hopefully theres a more experienced priest to answer your questions. 
Shadow is extremely good for Arenas and not bad for RBGS.
Also shadow right now is a pretty good 1v1 spec.
Holy is S tier pvp healer for arenas this season but will get nerfed pretty hard next patch.
Discipline is A+ this season and seems to be getting good buffs for next patch so gonna be a strong pick for arenas. It’s also really good for RBGS.
For M+ both healing specs can do 15s easily. Holy has some bad community perception but is a strong pick for high keys. Disc has better community perception and struggles on high keys if the group is not that good.
Shadow does tons of dmg but lacks utility which makes it a not much desirable spec for M+ comps.
So yea Priest is a nice class to main. Maybe if you want to focus on DPS it might be tricky since at the end of the expansion maybe shadow gets mega nerfed and you only have 1 dps spec option, so mind that.
Priests pluses (as far as the healing specs go):
a. It’s the only class with two healer specs. Arguably, one is the easiest in the game, the other is the hardest.
b. Disc is a very different kind of healer to most others in that it has an important pre-emptive requirement to master. This is novel and along with the ability to do healing via damage and its absorbs it puts disc in a class of its own.
c. In pvp disc has a strength no other healer has. It has two schools of healing–holy and shadow. Hence, the other team can struggle to shut your healing down short of killing or sheeping/stunning you.
d. Disc has strong damage reduction and cds. But this can be both a boon and a minus if you don’t know what you are doing.
e. The two healing specs give you more options for healing. On some boss fights in raids having both available can be a strong positive.
Negatives:
a. Holy gets a bad rap, but it does come up short on utility. It makes up for this though because it can pump some high hps numbers, especially in heroic raids in large groups.
b. Disc has some serious mana issues in SL. You can get help via innervates and your dps using defensives and staying out of fire will help. But bring mana pots for sure.
c. Mobility is not a priest strength. It’s not like you have zero options, but in M+ your best HPS healing where you can really pump comes from Shadow Mend for Disc and Heal for Holy (with Flash Concentration Legendary). Unfortunately neither can be cast on the move. In both cases though you do have other options, but none that can pump sustained healing nearly as much. Also, skill can make up for this weakness in at least some cases.
Just a few thoughts that stand out to me the most.
I have over 300 days played on this priest despite not playing for a decade at one point. Def my main.
I played my rogue since TBC, and recently I decided to level a disc priest. I only do PvP stuff. Now this priest is my new main. It’s just so much fun to be a DPS-healer. I never realized I would love playing disc so much. So, to answer your question, yes, a priest can be a great main.
Disc pretty tanky? What aspects do you like about it?