I don’t know which is more in use, but I would guess Z-Wave JS UI is still more popular.
I don’t think there is a reason to switch to the core add-on unless you are literally starting over. If you no longer want to use the UI in Z-Wave JS UI, then you can just pretend it doesn’t exist. From HA’s perspective they are the same Z-Wave driver and you can just use HA’s UI. Currently both add-ons are maintained equally well.
IMO Z-Wave JS UI still wins in comparison to the core add-on, but the advantages are fewer than they used to be:
- HA doesn’t support Association groups
- ZUI’s network map is much better than HA’s, and provides health check and debugging capabilities. HA’s network map is just a visualization at this point
- ZUI’s network map also lets you set priority routes, no support for priority routes in HA
- Replace failed node, HA only supports remove failed node
- HA doesn’t provide the ability to use custom device configuration files (usually only needed by developers)
- You can run Z-Wave JS driver javascript code directly, which allows you to do things HA doesn’t support
So besides the group associations (which is kind of basic functionality HA lacks) the rest are just better troubleshooting tools.
Advantages of core add-on:
- Maintained by HA devs, i.e. “officially supported”
- Easier installation (but this is a one time thing)
- Easier controller migration (NVM backup/restore) (but this is a rare procedure)
So it really depends on how much you need debugging capabilities, IMO. If you want to switch to the core add-on, you can attempt to do the reverse of my guide: Switching Z-Wave JS Addons with Minimal Downtime! Z-Wave JS (Official) to Z-Wave JS UI (Community)