I always feel like Blackbeard isn't nearly as strong as people think. Cuz he relies on his devil fruits and his crew rather than try to get stronger the hard way. Also, he's clearly cowardly otherwise he wouldn't have ran away from Rayleigh, or attack whitebeard while he was injured and weakened, or set Gekko Moria up and gang up on him with his crew..etc. No way I'm choosing him among the top 5. In fact, I would be disappointed if Oda uses him as the final boss...cuz he's a weakling.