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

Before Flex became popular (around 2014), 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. As of writing (2020), flex is the recommended approach for building grid systems and has decent browser support.

Have you ever used a grid system, and if so, what do you prefer? (Cont...)

For the adventurous, they can look into CSS Grid Layout, which uses the shiny new grid property; it is even better than flex for building grid layouts and will be the de facto way to do so in the future.