I’m working on a new plugin and I’m wondering if it should be a panel or a dialog or both.
Questions:
I think it really depends on the kind of plugin. If one can say “I run the plugin”, I usually go for a modal, as this implies one action that I can then trigger with a shortcut, select my options and “run” it. When a plugin, e.g., shows information about the scenegraph, however, panels would be my go-to option (as then, having it open while clicking through the scenegraph is essential).
For my two plugins, I’ve kept my modals since they are purely action-based (“Insert placeholder text”, “Export text”, “Search and Replace”, etc.). For my new plugin (Markdown), I support both. I have a modal for “action-based” things, and a panel that allows clicking through the scenegraph and editing the Markdown version of a text layer one selects right then and there.
All in all, I’ve only had one user requesting me switching to panels (which, considering the amount of support requests I get, isn’t much at all). In the end, one should, in my opinion, decide from a UX point of view what’s better, with the following questions being essential to me:
The one thing I find irritating is that most plugins “moved” to panel-based UIs (regardless of the kind of plugin) as soon as it was released, seemingly because it is the new fancy thing 
. I think no decision is wrong here, as long as one does it for a reason other than everyone doing it (or it seeming more fancy).
Just to back my statement up a bit (leaving a statement without any references bugs me a bit 
) , here are a few quotes from the official recommendations in the plugin-docs:
If the user needs to have access to the canvas then the plugin panel would be the best option, since it’s contextual to the users selection and allows the user to modify items on their canvas while interacting with the plugin UI.
https://adobexdplatform.com/plugin-docs/design/ux-patterns/panel-ux.html
If the plugin needs to run an action before the user starts a new action then the modal would be recommended for that use case.
https://adobexdplatform.com/plugin-docs/design/ux-patterns/modal-ux.html
Are you interested in converting your plugin’s modal dialog box UI into a panel UI? Keep in mind that not every modal dialog flow is a good fit for this change.
https://adobexdplatform.com/plugin-docs/migrations/how-to-migrate-from-modal-to-panel.html
One last thing I consider is the ability of quick prototyping (something that, to me, is incredibly important when developing plugins as I can then see whether an idea is even feasible to implement). With panels, there aren’t a lot of libraries making this easier. Almost all my plugins using modals, however, now work based on my xd-dialog-helper library (shameless promotion 
), which means I quickly “sketch out” a dialog in the WYSIWYG-editor, download the code, and already can start working on the XD side of things. Later, I can still polish the dialogs if needed, but I’m actually at the speed where I’ve developed a lot of mini-plugins for repetetive tasks I had to do in a few minutes each (including UI with options to select)… For “real” plugins, of course, this gives me more time polishing and testing the plugin.
Nice editor! 
And good points!
Thanks for the great summary Pablo. You were quick to grab these new design docs 
They were published about 16 hours ago with the site redesign.
cc @dcaicedo, who spearheaded the effort to get make the design docs and resources available.