Both options will work. However, be aware that if you choose to select and mark the text with box function, there is a higher risk of inaccurately select elements or unwanted text that will then be part of the fact value within the iXBRL file.
If you choose the text-selection function, you will be able to select more precisely the text to tag. It is therefore recommended for tagging individual words and small paragraphs.
Finally, note that depending on the layout of the report (e.g. you have multiple columns) you would have to tag each column individually so that the text in the 'fact value' is displayed correctly.