Definitely Paper. Working with Fabric often requires you to get your hands dirty at the compiled bytecode level, which is very powerful for mod authors but real

Definitely Paper. Working with Fabric often requires you to get your hands dirty at the compiled bytecode level, which is very powerful for mod authors but really increases the floor for "actually building something that's fun to use" in a way that will probably just be very frustrating for new programmers. Forge is focused on client-side modding which is just inherently trickier and requires more awkward APIs. Paper really gets out of your way and lets you program basically whatever you want to do server-side without worrying at all about needing to install mods client-side. I would't worry at all about capabilities—minecraft is an extremely flexible program, especially with the chat commands system, and you can still create cool custom UIs and behaviors without touching client-side code at all.