Board Thread:Boruto: Naruto the Movie/@comment-24992241-20160112202210/@comment-2005101-20160114182600

Omnibender wrote: Then, during his fight with Gaara in the Chunin Exams, when he uses Chidori for the first time, Kakashi says the reason he wanted to train Sasuke was because he was the "same type" as he was. Many presumed at the time that Kakashi was referring to the fact that they both used the Sharingan, among a number of other similarities. That could still apply.

Raiton is indeed the safest bet. He's been depicted as the Raijin opposite to Naruto's Fūjin, his strongest attacks have ended up being Raiton rather than Enton. But, oddly enough, the chakra nature he has an affinity with has never been definitively said to be Raiton.