#2 The Wyatt Family
Well, they are one of The Shield's oldest foes - and probably the most familiar, but there would almost definitely be a new dynamic if The Wyatt Family were to reform nowadays. With Harper and Rowan splitting off to become the Bludgeon Brothers - potentially WWE's most dominant tag teams in history - it's quite hard to think that the pair would be on their way back to the Wyatt Family, but Bray's mysterious powers could very well entice them.
Likewise, Braun Strowman has become a monster in his own right and is arguably now the Superstar of the faction. Would he be content playing second fiddle to the Eater of Worlds?
If the Wyatts were to reform to face The Shield, it would probably be a very different Family to that of the previous rivalries, but with Rowan and Wyatt's partner Matt Hardy sidelined, Strowman could call on Wyatt and Harper if he needs fresh partners for his fight against the Hounds of Justice.