u/Large-Dot-2753 is pretty spot on about the importance of a variety of primary sources in any historical investigation, even when they differ as these variations could be interesting and elucidating in an of themselves.

The only thing I'd add is that when judging a single source, the more we can know about the source the better. If we're considering a poem an old french poem from the 11th century, the more we know about who wrote and how it came to us allows us to better judge how we should treat it as a source. With regard to the physical source, do we have the original production? If for example the earliest edition is in Latin from the 16th century , or if the oldest are similar but not identical later variations of the same source poem one would have to critically take into consideration the way the source may have changed and the effects that might have on how it is used.

Even if the oldest edition we have is known to have been written in the authors hand, any information about the author helps put the source into perspective. Who was the author, why did they write it, how might their viewpoint be limited or unique or be considered in comparison to another source of the same era/topic. Even if a source is clearly not consistent with what the rest of the historical record tells us, knowing about the source and its author allows historians to better judge it for its merits and flaws, and compare it with other sources.

For example if we know everyday life for mid 14th century peasants in Southern Europe was less than pleasant, a source telling us about how the local populace had never been better can be very useful if we know about the context in which it was written. In this case an official writing that to the governing authority tells us a lot about the relationships between administrative officials and polities that ruled over that region, and possibly between the common people and those who ruled over them, even if much of the facts of the source are without any basis in reality.

What is most helpful in determining what everyday life was like for an average person in the past is a variety of sources. But in considering the utility of any one primary source, the more knowledge about the source itself is generally more important to how useful a source is than the type of source it is (state sanctioned annals, poems, shopping lists), as knowledge about the source and its author is the most important factor to a historian in being critical of the information it contains.

I'm afraid this is very much an 'it depends' answer, but also one where 'more sources, the better'.

If you were eg wanting to know how an ordinary person cooked a meal in 1700 you could look at recipe books, descriptions of meals, pictures showing every day life, actual pots and pans themselves, advice on how to preserve food, ettiqutte text books, archeology (to show what was actually stored and how) etc etc

If you wanted to know what eg a fish wife in Bristol wore in the 1500s, you would look at pictures and wood prints, statues, written descriptions, diaries, laws such as sumptuary laws, any still extant textiles etc etc

For 'every day life' relying on a single source is usually problematic, multiple sources of different natures are more reliable and allow you to consider potential inaccuracies or gaps in other sources