Bb is probably stronger..As a Shanks fan, I have no problem with Shanks being the weakest Yonko..Bb ads are really more exciting
Haki is stated to be supreme in this universe. Teach relies on Devil Fruits and broken abilities, the same way Moria did.
Blackbeard is a coward who betrayed the people who gave him a home and family.
Shanks gave his arm up to save a boy who he thought of as a son.
Shank's Haki rolls Blackbeard, IMO.