I really like the way you can choose whatever measurements you want to use in the WordPress 5.9 right hand toolbar. The feature is not available everywhere yet, but It’s very handy. Generally, I use REM and variable units like % as much as possible, where appropriate, over Pixels, because then the responsive aspect is built in.
I’ve been very much influenced by Kevin Powell‘s approach to responsive layouts. As such, I’m actually controlling the sizes here via the extra CSS in the Child Theme, but you can also change some things in the beta editor.
As you can see, in the dropdown menu: PX – % – EM – REM – VW – VH
All About Units
This video helped me get to grips with all the units available in web development.
You get a lot of extra control with the Kadence blocks – take a look.