Both. Amazon gives you the option to use a standard text link that you deploy within your text, as well as providing a plethora of widgets to choose from. To add variety and visual interest to your posts, it’s best to use both.
The widgets are essentially like mini adverts that you can use to add a little visual spice to a post. As an example, you could opt to add a text and image widget at the end of a product review to give readers a visual of the product. This helps to grab a reader’s attention, especially if they’ve just skim-read your words. As such it’s more likely that a skim-reader would click the widget rather than the in-text link.