Dragon has the most hype as the government's worst enemy, but that was
before BB made himself known, not to mention that probably doesn't directly
originate due to his strength. But exactly what his title says, being a threat to the
World Government actively, there's really been no other pirates who outright challenge the
WG aside from Luffy and even then Luffy doesn't revolve around taking it out.
Thus far most of his threat seems to come from tampering with the government's
countries by supplying rebels, erasing the government's control over countries
doing so, along with him having followers with the same goal scattered throughout the globe.
Neglecting that for a second, I think BB has more hype going for him.
Having a fruit that nulls someone's ability and can suck in everything, is arguably
the most OP fruit, combined with the force of White Beard's hax fruit.
If you can't get to high ground- you're going in, if you get close and attempt to engage,
he can take away what's probably your most valuable attribute, and even from a distance
his Guru Guru is shaking the earth along with you.