Which layout system should you use for a complex two-dimensional layout?

Using CSS Grid is the ideal choice for creating complex two-dimensional layouts. This layout system allows for the design of both rows and columns simultaneously, making it particularly effective for intricate structures that require precise alignment and spacing of elements. With CSS Grid, designers can define a grid template and assign elements to specific grid areas, enabling a high level of customization and responsiveness.

CSS Grid supports advanced features like grid areas, auto-fill, and auto-fit, which enhance the ability to create layouts that adapt to varying screen sizes and content amounts. It simplifies the process of aligning items in a two-dimensional space compared to other methods.

In contrast, while CSS Flexbox is useful for one-dimensional layouts (either in a row or a column), it is not designed for handling more complex grid structures where elements need to be placed in multiple dimensions. Float-based layouts are outdated and can lead to difficulties in managing spacing and clearing elements, while a positioning system can be overly rigid or challenging to maintain for responsive design. Thus, CSS Grid remains the most effective and modern choice for complex two-dimensional layouts.