Two videos about the Auschwitz gas chamber…which is correct?

Here are two conflicting versions of the story of the Auschwitz-Birkenau gas chambers.  The first video shows the ruins of Krema II at Auschwitz, as a tour guide speaks to a group of tourists, who are not shown.

The second video was done by the famous “denierbud.”  It also shows a depiction of Krema II, one of the four gas chamber buildings at Auschwitz-Birkenau. Whom do you believe?