Druid or shaman. However Shaman has the most interrupts, useful totems, good off heals on their respective dps specs, hex for cc, real bloodlust and they can reincarnate.
You’re going to get a lot of answers, and people’s opinions will differ. For example, I see everyone recommending Rogue. Rogue is good in M+ typically, but I wouldn’t say they have such amazing utility that they’re an obvious pick. I think people get tunnel-visioned by how unique Shroud is. Stuns/CC/immunity are good, but also found in other classes (Hunter, for instance, matches very handsomely on paper vs a rogue and also bring Hero/Lust. Which isn’t to say Rogue isn’t worth bringing over a Hunter, just that it’s not nearly as clear-cut as point seem to think)
Druid has a lot of possible utility in M+, but will vary wildly based on spec and talent choices. Druids offer virtually nothing in raid utility, and it’s a sore sticking point.
I think rather than looking for a “best” utility class, the important thing is to not pick a class with low utility. These “wrong answers”, for me are:
Warrior. You bring Battle Shout and a “healthstone” effect which, while powerful, does not make up for the complete lack of any other useful abilities. Most raids want one, but that doesn’t mean they have a lot of utility
Warlock. Warlocks have a rough time in M+ comparatively. In raid they are often in high demand for their gate and healthstones (but let’s face it: PUGs want 'em for summoning).
[Havoc] Demon Hunter. Effectively zero utility. Don’t do it.
Death Knights. “Slappy hands” is neat, but only good for this expansion, and Deathgrip/AMZ is powerful, but as with warrior, you will feel the lack of other skills.
Brez
Typhoon
Ursol’s Vortex
Treants
Remove Poison/Curse
Innervate
Entangle
(Mass Entangle or Bash)
Off Heals
Ranged
Can taunt
Uncapped AOE
Heavy Burst damage
Whatever Racial utility they may have
BASELINE:
Earth elemental
Tremor totem (fear remover)
Purge
Slow totem
Bloodlust
Ghost wolf
Best interrupt in the game
Remove curse
Off heals if not resto
Talented or spec
Sundering interrupt
Speed totem
Root totem
Res totem
I’m probably forgetting some.
I’d say druids are up there as well specifically boomkin as the poster above said
Warlock actually have some of the better utility, and much of it completely unique. You’d almost never do progression raiding without at least one, even if their damage is terrible:
Healthstones (totally unique)
Gateway (totally unique)
Brez which can also be used preemptively
Summons ofc (incredibly desired for pugs, and most guilds seem to be in need of one as well)
Almost always have one top-tier damage spec, and in niche forms (either top cleave with Destro or top spread with Aff)
Mages are another, in that they have some CC, a cheat death, an immune, top-tier mobility, Lust, and are also always near the top of damage.
Boomkins as most are saying are great, CC, unique CC (vortex), treants for M+, best spread aoe & great single target/cleave, innervate, brez.
Rogue is being mentioned quite a lot, but they were actually not used at all in the world-first race from their lack of utility/average damage. They have some CC, but that’s about it, other than Shroud for M+.
SPriest has a bit of utility, in that they bring PI, grip, Disperse can trivialize some mechanics, good spread damage.
If you’re looking for a desired class with lots of utility for raiding/M+, it’d be Druid or Mage, Lock if you mainly raid.
Druid and Shaman are easily the two most useful classes in group content.
Druid has a little more utility like Stampeding Roar, Typhoon, Vortex and Rebirth, they also can dispel poisons as baseline which is possibly the most common type of debuff.
Shaman utility isn’t as vast but it is very unique in Purge, Bloodlust and Wind Shear, Earthbind Totem is an AoE slow with 66% uptime which is something tanks love.
Paladin also has a lot of utility but isn’t neccessary as frequently as a Druid’s or Shaman’s.
I don’t even understand why a lot of people are saying Rogue, they have plenty of CC and shroud but those are rarely necessary in M+ and completely useless in raids. If I were to pick a melee for it’s utility it would be DK; they have grip, brez and AMZ.
What support do we, as Rogues, bring to anything? A blanket stealth that I have NEVER used. The only thing we bring is if we happen to be engineers and have jumper cables on us use after we vanish out of a crap pull…only they haven’t been a thing in over a decade!