Kefla probably stomps. Broly's feats prior to going to his limit against SSB Gogeta don't suggest him to be on par with the ToP's upper-high/top tiers prior to it, whereas SS2 Kefla shouldn't be leagues below the level of MUI Goku/Limit Break Jiren. Not even SS3 is going to change the outcome, beyond making the fight go a bit quicker.