Right now I am editing my psjs files in vscode then switching to the UXP Developer Tool, hitting debug script, then choosing the file I want to debug. Is this currently the best way to do that? Would it be better to have a test plugin that runs my script?
I would develop in a plugin context, yes.
Sometimes that means just running in a snippet in UDT.
Do keep in mind the differences between script and plugin.
The only upside to putting your script into a test plugin would be that you could “Watch” the file, and UDT would automatically run the script again when you make changes to the file. If you don’t need that, I don’t know that the test plugin workflow is worth the overhead.
If you just want to run the script quickly, I think it’d be easier for you to attach the script to an Action and run it directly from Photoshop: https://developer.adobe.com/photoshop/uxp/2022/ps_reference/media/uxpscripting/#running-a-file