#2 Seth Rollins and his disciples

You know what they say, one man's loss is another man's gain.
In this situation, it's one faction's loss and another faction's gain. A few weeks ago, Zelina Vega and her group decided to cut ties with Austin Theory, as they took out the former Evolve Champion, marking the end of his tenure with Vega's faction.
Female superstar says she inspired John Cena turning heel HERE
However, later the very same night, Seth Rollins received a surprise, as Theory decided to help the former and Murphy in taking out Aleister Black on RAW. This led to Rollins embracing with Theory and welcoming him into his faction. In bolstering his numbers, Rollins now has two men who could join him in a feud with The New Day.
Personally, I loved the decision to put someone as young as Austin Theory with Seth Rollins, and Murphy, who despite being in his early 30s, has experienced a lot in WWE so far. Also, with the absence of Akam and Rezar (AOP), Theory is a much-needed addition to Rollins' group.
And how could one possibly hate their cool attires? The trio look as though they belong as a faction, much like The New Day with their trademark matching gear.
A major threat to The New Day
Like I had previously mentioned, The New Day remains as the most experienced faction in all of WWE but despite Rollins' stable being in their early stages, I believe that on the main roster, 'The Monday Night Messiah' and his disciples are the biggest threat to Kofi and his stablemates, in terms of a faction Vs. faction war in WWE.
A feud between Rollins' new group and The New Day could produce some of the finest 6-man tag team matches in WWE history, something similar to what The Shield, Evolution, The Wyatt Family, and The O.C. have pulled-off in recent times.