Hotspot is closer to what Oracle uses, so i would use that, although i’m not sure what Openfire is more compatible/optimized with. But i had cases when some apps only work with Hotspot variant.
To swap stop Openfire, rename the jre folder inside its installation folder to say ‘jre-old’, then install AdoptOpenJDK and run Openfire. If something goes wrong, just stop Openfire, rename jre-old back to jre and run Openfire. Later you can even delete that jre folder and use installers without Java included. I think Ignite Realtime at some point should get rid of installers bundled with Java anyway, because of licensing and to make producing the installers easier. Just one type and let the users install the Java.