The problem here is that while the Bismarck may have been a smaller ship it had a better crew, better fire control, better firing rate and better damage control.
My personal belief is being hit by a 15 inch shell is probably not all that different to being hit by an 18 inch shell, no matter what you are riding in it will still hurt.
I will still go with the Bismarck.
Yamato and Musashi's designers actually had planned a new solution to the problem of long range accuracy.
The solution involed launching a special spotter float planes from either of these Battleships hanger to fly ahead and spot for the enemy vessel.
The Yamato for example, with her 18 inch guns could fire literally over the horizon beyond visual range, which would be limited by the curviture of the Earth.
The duty of the float plane and her crew were to act as forward artillery spotters and relay target information and battle damage assesments to the gunnery and spotter towers onboard the Yamato/ Musashi.
This method of targeting would have in theory negated any direct surface threats to the Yamato/ Musashi by allowing them to use said curivture of the Earth to protect them from return fire.
However as stated, this system did not make up for lack of advanced fire control computers (for the time) that their American and German counter parts had.
And the float plane spotter method quickly broke down in combat due to the U.S. Navy acknowledging the importance of air superiority. The U.S. would and did make short work of any Japense spotter planes with combat air patrols launched from carriers miles away, once the eyes of the Yamato/ Musashi were out, the U.S. would and did on both occassions move air forces in for the killing blow.
As for the Yamato class's armor, yes the Bismark's guns were more accurant and still very deadly, but U.S. Navy testing of Yamato class armor after the war concluded that her turrets even on a direct hit from a American 16 inch gun, would not have effectivly penetrated thus creating the deadly "cartwheel" effect.
Although the latest type of U.S. 16 inch Mod 8 AP shells did do this at a flat trajectory in tests conducted in the Washington Naval Yard in 1946, but the "penetration" of the shell was along the lines of severe cracking of the plat, at a almost point blank flat angle, not a higher angle as what would occur in a gun battle at sea.
Also, like the armor of a Tiger Tank for instace, once you invert the armor plate to 45 degrees, any shell would have to travel further to penetrate.
Japanese steel even without the qaulity provided STS steel enjoyed only by the U.S., would have held up.
The Bismark in terms of armor, excelled at one thing, and history proves this. Her desingers took operation experaince and cues from operations during the battle of Jutland in the North Sea decades earlier.
The Bismark's armor was laid out to be a vertical wall surrounding her vitals. This was to hold with not only stresses of operating in dangerous North Sea weather , but if the British , who's navy was centered around large captial surface warships should engage her with naval gunnery, then shells would not be able to pass through her internals easily at flatter trajectories.
This made her vulnerable to air attack, but the British navy did not delpoy large carrier fleets in the North Sea, as the weather would have made difficult operating there. Unlike the Japense who faced U.S. carrier threats in almost every major naval engagment after Midway.
In all, it all comes down to terms of shot placement that the Allies delivered to the Bismark, and Tirpiz, what it took, where is was delivered, and upon how they sank.
Do the same for the Yamato and Musashi.
Then we start to get a clear idea of what each ship could have taken. Also their wrecks are also indicators of where major structual weaknesses could be found on each ship.
Except for Musashi...As she has yet to be documented on the ocean floor.
And the Tirpitz, as she was broken up and salvaged.
