1.) Personal opinion, unchallenged holds the field, and usually wins the field. Hence Tradition, Religion, Authority, Social Pressures, "Common Sense", Received Opinion, Textbooks, unsupported Lectures, Cultural Norms, Personal Bias, etc -- when unqustioned, will Rule our Lives BOTH as we agree, or as we disagree. There are no other alternatives.
2.) Seconary Sources trump personal opinion, depending on how established and accepted the authority of the Secondary Source, and the first alternative appears.
3.) Many Secondary Sources that agree with each other trump only one opposed Secondary Source, especially if the one is marginal, i.e., does not square with "common sense". Numbers and authority being equal, the Secondary Sources on the side of "common sense", "received opinion" and/or any from the list in #1 take precedence.
4.) The above is 'low school' -- the discipline of History in Higher Education requires the evidence of Primary Sources. Any Primary Source but the most marginal will usually trump any array of Secondary Sources. But One against Many do not trump at all times, depending on bias and the power of the Secondary Source Array.
5.) Many, Reliable and Corroborating is the goal of presenting Primary Sources to convince the reader of a conclusion. This is the ususal method and trumps all the above. Reliability is wrapped up in the "Critical Discussion" of each particular Primary Source.
6.) The simple presentation of Primary Sources often does not obtain the objective of "speaking for themselves" with accuracy. Readers sometimes Think or Wander. They may need guidance to arrive at the aimed-at conclusion, so Primary Sources Explained and Related to the Point at hand is the Best Presentation.
7.) With many Primary Sources, the Explanations will often be in terms of other previously presented and explained Primary Sources so as to underline Corroboration and Number, assuming Reliability has been established.
8.) Presenting the Primary Sources of the Opposition Side well usually strengthens the original argument. Readers sometimes Think or Wander. If they stray into Opposition Territory without guidance, they may be captured, or at least, become suspicious of the original argument.
9.) Presenting the Whole Case, with its sub-arguments on various sides, including a discussion of the Reliability of the Primary Sources and how Secondary Sources do and do not relate to the Whole Case, and to individual Primary Sources, is the Best Procedure.