I also run Surge on jungle Kayle. It ensures that you can win an early game duel if someone tries to catch you at a buff or counter you (or might scare them into thinking you can) because most other junglers will be carrying flash.
I don't recommend dueling anyone as early-game Kayle, though, things can easily turn bad for you, especially if their team is observant and comes to help. I just focus on farming the jungle and ganking heavily, since the decent movespeed slow and the awesome damage are all most laners really need to get a kill. Lategame I love catching carries roaming their jungle and melting them before they can even react.
Ever since Stark's Fervor was removed though I've been messing with builds. Right now I'm at Wriggle's -> Zerker -> Cleaver -> Malady -> Rageblade -> situational but I might start swapping Rageblade/Malady. I also want to experiment with different rune pages, right now I run AS red/blue/quint and I think it's a little overkill
edit: I haven't tried to make Kayle work in any other slot so I don't know much of the theory, but people definitely sleep on her, I hate that Riot keeps talking about another complete rework
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