What should you start with to customize your Mendix application effectively?

Starting with Mendix AtlasUI is the most effective approach for customizing your Mendix application because AtlasUI provides a solid framework and design guidelines specifically tailored for Mendix applications. This includes pre-defined styles, components, and layout options that align with modern UI/UX standards. By leveraging AtlasUI, you can ensure that your application not only looks aesthetically pleasing but also maintains consistency across different screens and modules.

Using AtlasUI allows for quicker development since it reduces the need to create styles from the ground up. You can customize existing components rather than building everything from scratch, which can be time-consuming and may lead to inconsistencies in design.

In contrast, building from scratch may lead to a lot of redundant effort and could hinder the project's progress, especially for teams that may not have dedicated design resources. Integrating third-party libraries is also a valid approach but often adds complexity and may not integrate seamlessly with the Mendix platform, potentially leading to issues down the line. Removing existing styles can create a disjointed user experience and may result in losing important UI elements provided by Mendix.

Overall, starting with AtlasUI not only streamlines the customization process but also ensures a more cohesive and user-friendly application design.