Which is most credible?

That depends on what question you are asking.

If you want:

original evidence

→ documentary editions are often strongest because they contain the actual documents.

If you want:

historical interpretation

→ a strong scholarly monograph is often most valuable because it analyzes evidence in depth.

If you want:

the latest specialized debate

→ peer-reviewed journal articles are often best.

So there is no universal ranking.

Different sources perform different functions.