Hey everyone!
(This topic is to share what I learned about which class/spec best suits Tidesages. 
People are more than welcome to share their thoughts too.)
So I wanted to play a Shaman for Dragonflight, and thought to myself “I need to figure out what race I liked the most”. Most of my characters are dwarves, so I naturally went for that here too… But I just had this feeling of wanting to try something “different”, since playing Dwarf constantly can get a bit dull.
Now… I am a big H.P. Lovecraft fan, and I remembered that the Tidesage storyline in BFA, had a very “The Shadow over Innsmouth” (Lovecraft story) feeling about it, so I started researching about Tidesages! 
The classes I have found to suit the Tidesages are:
- Mage (Frost/Arcane)
- Priest (All specs)
- Shaman (All specs, but especially Resto)
- Warrior (All specs)
After doing my research I came to this conclusion…
Who are the Tidesages?
A quick recap for people who needs it. The Tidesages are a a religious group who all worship the Tidemother, who is a being from the sea that whispers to the Tidesages. It is only through hearing the Tidemother, that you can become a initiate and join the Tidesages. It isn’t specifically stated anywhere, but it is assumed that the Tidemother is an elemental being.
The Tidesages study to master command over the sea, and although they control ALL the elements, they especially focus on mastering water, wind, and the storms. Their duties include blessing the Kultiran ships, fishermen and their equipment, reading good/bad omens, and praying for the sailors at sea. There will also always be one Tidesage on board of a Kultiran ship, to help the ship along it’s way by controlling the elements.
Most Tidesages will be robe wearing casters (cloth armor), but some also wear heavy armor. Heavy armored Tidesages are referred to as Shrine Templar (paladin-like melee fighters), and Warriors that guard the Tidesages are referred to as Ironhull Apprentices.
Classes and how they suit the Tidesage fantasy…
General thoughts…
Let’s address the elephant in the room… Cloth armor goes well with the Tidesage look, and especially the rare Vestments of the Tidesages set that drops from Shrine of the Storm is a full on cloth Tidesage set. Because of this I hear most people say that Mage or Priest is best fitting the Tidesage fantasy, where as Shaman or Warrior would be more of a Shrine Templar/Ironhull Apprentice.
However if we ignore the armor for now, and only look at “Tidesage abilities and their professions”, then Shaman and Priest fantasy are by far the best fit with what Tidesages are. A Tidesage has two main tasks… The spiritual and more religious aspect where they bless and pray, and the more physical aspect where they control the elements, with special focus on water, wind, and storms (3/4 Shaman elements).
Frost Mage is a very popular player choice, since they can conjure a water elemental and use Frost magic, as well as Arcane Mage since you see Tidesages during the Stormsong Valley storyline using Arcane magic. At Addington Shipyards we also see “Tidesage Innitiates” with water elementals.
Additionally, if you go to Stormsong Valley and fight the enemies, you will see them use Shadow magic which is a Shadow Priest focused playstyle. Of course… This is after they get corrupted by Lord Stormsong. Also, if you look at what Brother Pike (the Tidesage NPC) does when he helps out in combat, he uses a mix between water/sludge and holy magic.
Best class/spec for Tidesage RP
First off I’d like to say that RP is of course “roleplay”… So you can roleplay anything you want, since RP shouldn’t be too set in stone. Any of these classes suits the Tidesage fantasy, and none of them are a “wrong choice”.
With that said, my goal here is to give a “hard objective look” at the classes and their specs, to figure out how well they naturally fit the Tidesage fantasy.
Objectively, Mage only has two aspects that goes well with “being a Tidesage”. Which is that you have a water elemental, and you wear cloth armor. The fact that Frost mage uses Frost magic, which is “technically frozen water”, is a bit outside the Tidesage fantasy which HARDCORE focuses on water, wind, and storm. Ice certainly fits within that, but it’s such a niche and small part of their overall abilities.
Priest is a VERY good fit for a Tidesage fantasy. Although lacking elemental spells, they do fit 50% of the Tidesage fantasy, with their religious nature. As well as the fact that you can RP a corrupted Tidesage using the Shadow Priest spec, which is a 100% fit to that fantasy. And lastly they wear cloth armor, which is what they are visually most known for.
Shaman is a odd one, which has become a bit easier to fit 100% to the Tidesage fantasy as we got Shadowlands… Shamans use mail armor and would be considered more of a Shrine Templar, which is the Kultiran equivalent of a Paladin. and less of a “Tidesage Priest”… However with Shadowlands, we now have the option of wearing “cloth like armor”, which isn’t armor specific. Meaning as of Shadowlands you can put cloth MOG on your Shaman, without having to equip actual cloth gear.
Conclusion
Of course if we ONLY focus on RP without worrying about Shamans wearing cloth gear to “appear” as a cloth wearer, they would 100% be the best RP choice IMO.
But if we wanna be able to “RP as we play WoW normally”, which would require the proper armor type gear, then personally I think that Priest is the best Tidesage cloth option, and Shaman is the best Shrine Templar choice, while being a “decent” Tidesage priest.
Hope this read and research helps new RPers get an overview over the classes and how they objectively suit the Tidesage fantasy.