suanLoBeach It is difficult to answer the question of which is easier to use, as the opinions will vary considerably from person to person, but in terms of which is more powerful, the spine-unity runtime is simply more flexible and can do more. You can clearly see this by looking at the number of official examples we have. It is very easy to install and view examples of spine-godot, so we recommend that you check it out first.

suanLoBeach By way of background, the spine-unity runtime has been available since 2013, whereas the spine-godot runtime was only released in 2022. Compared to the spine-unity runtime, which has had years to develop and integrate various features, spine-godot is still relatively new and lacks some functionalities.

Perhaps you might want to take a look at the Godot-related issues in the spine-runtimes repository:
EsotericSoftware/spine-runtimesissues?q=is%3Aissue%20state%3Aopen%20godot

There's a dedicated person doing the Unity runtime, while the Godot person also supports multiple other runtimes. As a result, you can get your Unity bug fixed within a working day, while Godot's bug response times take considerably longer for understandable reasons. Unity is just a more popular and more mature platform in general.

By adopting Godot, you also have to deal with worse support and integrations for all tools, not just Spine. It's a rather new engine with considerably smaller user base. We're already seeing increased demand for Godot support here and elsewhere, but that takes time to ramp up. You're basically an early adopter with all that entails.