I am betting on Yami.
Considering that Luffy and BB are polar opposite to each other, it's likely that this holds true even when it comes to their dfs.
Here's the portrayal contrast between them.
- Nika is symbolic to Joy - Yami is symbolic to despair
- Nika is dawn - Yami's darkness is infinite night or a void.
- Nika has bright white glow - Yami and BB have dark, black theme going on.
- Nika gives freedom to manifest as per imagination - Yami takes other people freedom of power and movement.
- Nika's awakening makes surrounding bouncy - Yami's awakening can crush surrounding (Blackholes are known for their immense gravity)
Yami has always been portrayed as special case of Logia.
It's awakening could add some God tier touch to it. He's likely to be Earth God or Moon God (I think Earth God is more possible based on his dream of King of the World)
Three God fits the bill.
Erebus / Chaos (Greek): The primordial deity of night and dark void who existed before light. Erebus doesn't just block light; it actively swallows all matter and energy.
Apep / Apophis (Egyptian): The giant serpent deity of darkness and chaos who attempts to swallow Ra (the Sun God) during his journey through the underworld every night.
Tsukuyomi (Shinto): The God of the Moon who killed the food goddess out of disgust, contrasting sharply with Amaterasu (Sun).
I think Yami's awakening is the one which will cement BB as some God tier being (he was specifically looking for yami for decades). Rest is just bonus.