Framework choice for AP CS A students: Swing or JavaFX?
Disclaimer: some do consider this a war like emacs/vim. I don't.
I'll quote you on this: &quot;I'm looking for something that allows students to get up and running relatively quickly and easily with something small yet meaningful&quot;.
From this: JavaFX. Along with IntelliJ, and Scene Builder, students can build a GUI very, very quickly. The FXML file which &quot;creates&quot; the GUI also gives an introduction to XML file structure.
It also teaches many Java 8 things. This is vague, but here are some examples:

A lot of lambda expressions.
Work with Collection. The students would need to use the collections in java 8, if they learn JavaFX. This is handy, because those classes are obviously useful outside of AP CS A
The Stream API (which gets buffed in Java 9, coming out soon) has a lot of usage as well in JavaFX.

I could continue this rant forever, but the main point is that JavaFX is self-dependent, which means that it only requires itself and java, unlike Swing, which requires AWT.
I hope this give you some idea about putting a GUI library in your curriculum.

As was pointed out in a comment, JavaFX has an added bonus: It's more likely to become the library your students would use, if their careers lead them to doing GUI in Java. I say this because Oracle said so:

6. Is JavaFX replacing Swing as the new client UI library for Java SE?
Yes.

The link contains more details, but the core of that part of the faq is that it is a replacement. (Which is in no way saying that Swing will not be included in future Java releases, because of backwards compatibility).