Lightning Web Components (LWC) provides a set of built-in base components that you can use to build your LWC. These components are optimized for performance and can save you time and effort. Here are some of the best built-in base components in LWC:

1. lightning-record-form: This component allows you to display and edit a record’s fields using a pre-built layout. It can be used to quickly create forms for creating and editing records.
2. lightning-record-view-form: This component allows you to display a record’s fields using a pre-built layout. It can be used to quickly create forms for viewing records.
3. lightning-datatable: This component allows you to display data in a tabular format with sorting, pagination, and other features. It can be used to quickly create data tables for displaying records.
4. lightning-input: This component allows you to create input fields of various types, such as text, number, checkbox, etc. It can be used to quickly create forms for capturing user input.
5. lightning-button: This component allows you to create buttons with various styles and actions. It can be used to quickly create buttons for performing actions in your component.
6. lightning-layout: This component allows you to create responsive, flexible grid layouts. It can be used to create layouts that adapt to different screen sizes and orientations.
7. lightning-map: This component allows you to display maps with markers and information windows. It can be used to create interactive maps that display locations and other data.
8. lightning-combobox: This component allows you to create a dropdown list of options. It can be used to create selectable lists of options for forms and other components.

These are some of the most commonly used built-in base components that LWC provides, but there are many more available to use, like lightning-accordion, lightning-formatted-text and many more. Salesforce has a wide variety of built-in components that can be used to build different features of your application, it is recommended to review the available components before starting to build your components.