I believe Imu will be the strongest of them all, requiring Luffy and Dragon to have to fight together.
As for Teach, I'm not sure because I believe that with his power he will nullify Luffy's Nika, so Luffy's victory will only be due to his skill with haki.
It's curious to think that only with Haki Luffy will defeat someone stronger than Kaido, but with 2 or even 3 devil fruits the possibility exists.
So I really don't know what to think about Teach's power.