All of you simpletons debating whether Carrot or Yamato will join are ignoring the ideal candidate:
Kin’emon. From the moment Luffy encountered his legs in PH it was clear that he was going to join.
His backstory is Oden’s backstory, in the same way Fisher Tiger’s backstory was Jinbe’s backstory but in this case, even more so for Kin’emon.
He was a delinquent/outcasts just like most of the SHs were during their childhood/young adulthood. And this was emphasized during the Oden flashback.
He has a great dynamic with the rest of the crew.
I’m telling you guys, the next SH is going to be Kin’emon.