What support scales the hardest for teamfights?
They should be decent in lane and fairly meta. From the top of my head I see Braum, maybe leona, thresh, nami, morg and others used a lot.
They should be decent in lane and fairly meta. From the top of my head I see Braum, maybe leona, thresh, nami, morg and others used a lot.
I say nami, morg, and braum
mostly morg because she can nullify enemy cc with her shield get 3 to 4 people in her soul shackles and use zhonya(if she has it)

They should be decent in lane
This is counter productive for scaling in team fights.
Also technically Soraka would have the highest team fight scaling of any support if she gets gold.
Queen Janna.
Depends what you're looking for in terms of teamfighting.
(Note: these are in no particular order, I just listed champs that I think are good at that aspect of teamfighting)
Initiation:
AOE damage:
CC/utility:
Peel:
In terms of overall viability you also have to take laning into account.
Not sure if you'd consider champs like Malphite and Ashe as "fairly meta" supports or not.
What support scales the hardest for teamfights?
Win rates for ARAM are tacked at LOLKING.
Considering ARAM is nothing but a drawn-out teamfight, I'd probably just look at those.

72.43% win rate in ARAM over the past month. Ever since Howling Abyss was introduced I've never seen her with anything less than a 65% monthly win rate (top 1~2 spot). She's pulled even further away from the top picks after her rework.