YC1 - Zoro
YC2 - Doflamingo
YC3 - Boa Hancock
YC4 - Enel
WTF?
Zoro is a Yonko himself but I get it since he is under Luffy command.
Doflamingo is nowhere near YC2 level.
Hancock is another Yonko herself.
Enel is nowhere near YC4 level. At least what we saw from him pre-timeskip.
My list:
Yonko Ally: Luffy(plot armor won't let me lose)
YC1: Zoro(pure strength won't let me lose)
YC2: Cracker (without plot armor from Luffy he is undefeated)
YC3: Shiki (because I guess he was YC3 of Rocks)
YC4: Yamato (because if Kaido had any YC4 could only be her, not that she is weak but it is clear the position of others)