Basically what options/tools you use to make your posts better or more readable/attractive for others is a matter of taste.
The name "Blockquotes" already explains that it is better to use them for quotations and citations.
Whether you use an enumeration like
- List item
- List item
is basically a matter of taste also unless you want to make clear that what you will list has a certain order or you consider referring to an item in the list.
Bold or italic text can be used to mark text parts and point at what you think is important.
As this site is about Islam and not programing the preformatted text:
enter preformatted text here is not necessary but can also be used to mark or point at text passages or parts you want to point at or consider important. I myself wouldn't use it at all, and I often find it misused for quotation and usually edit and replace those posts by using Blockquotes.
All what I have quoted above are recommendations in general and based on my own experience and practice.
Note that googeling the names and their meanings of these options or referring to Markdown help or Comment formatting would have helped you a lot to get your answer.