To determine the purpose of a text, the most effective strategy from your options would be thinking about the type of text you like to read.
Understanding the genre and style of the text can give you insights into its purpose. For example, if it is a persuasive article, the purpose might be to convince you of a particular viewpoint. If it is a narrative, it may aim to entertain or convey a message through storytelling. Analyzing the text type can help you appreciate its intent more clearly.
While considering your feelings before and after reading or where you heard about the text might provide personal context or biases, they are not as directly useful in identifying the purpose of the text itself.