Hands down the best? I think I’m torn between Persians and Spanish.
Spanish, the obvious reasons are: the trade team bonus, and the civ itself has solid options, knights, conqs in castle age, Paladin, Bombard Cannon, Bombard Tower, Elite Conq in Imperial, so they’ll be useful in terms of providing army. They’re also reasonably good on water maps.
Persians: le douche, douching a player in the enemy team is always a good way to change the meta and mix up the game a bit 
Portuguese. Build feitorias and spam bombard towers. Then, sling your allies gold and stone.
Also, the team bonus is very support-like if you coordinate during a drush
by the point you can start slinging your opponent enough gold and stone to be worth it with this strategy the game should long have been over.
I guess a siege monk push could kind of count as support? Neither unit are meant to really be the backbone of an army, they are hard to mass, expensive to upgrade and micro intensive to control. It’s a big load off at least a low to mid elo player if they don’t have to worry about those things themselves. I guess it would make some sort of sense to have a 3v3 team be one flank going scouts into knights, one flank going archers and the pocket going fast castle, a few immediate knights for maximum profit, followed as quickly as possible by going forward with siege workshops and monastries. Then bring in forward castles, help with a team wall, and later do trebuchets and/or bombard cannons too.
It’s not the meta, but with practice it can be a strong play.