Working with columns in Gutenberg is frustrating (with both these plugins) compared to a builder like Elementor. Both these plugins are a step forward from the builtin columns, but needs more work.

I hope that the Core team implement the column functionality of these plugins, but it needs to be more like what builders like Elementor has, where columns can be duplicated/deleted/styleCopyPaste, and it must also be easier to add blocks into the columns. Right now blocks can be created outside and then dragged into the column (using the drag handle on the left), but it would be so much better if the blocks could have been dragged from block select panel.

And the new block navigation panel helps, but it would be so much better if it was for the whole page (all blocks), and visible all the time (like Elementor).

As for what plugin is best?

Coblocks is better at resizing the columns. That it’s possible to select the divider directly without having to select the row is a huge plus. And that width of the columns is not stepped is also better.

KB has more options, just check the prebuilt library for what it can do (button at the bottom when adding a Row Layout block).