Have you ever used a grid system, and if so, what do you prefer?

The float-based grid system was the most reliable because it still has the most browser support among the alternative existing systems (flex, grid). Bootstrap was using the float approach until Bootstrap 4 which switched to the flex-based approach. Flex is the recommended approach for building grid systems and has decent browser support. But I am almost confident that with the broader adoption of CSS Grid, it will turn into the main layout standard.