As you have found, different folks have different opinions on this question, and to some degree it has been an ongoing project of this forum to delineate that difference (among other efforts to establish what exactly therianthropy *is* and is not, where it comes from, etc.). It's not always labeled so explicitly, but that difference does underpin many other, related discussions -- the recent discussion about language between the two communities
is one relevant example. The good news is, nobody expects you to read literally the entire forum to get up to speed, but keep in mind that there may not be a definitive, "textbook" answer for some of these questions. Even the ends of threads like the one already linked above still have folks with differing opinions, although they tend to be closer to a consensus than they were before the thread.
Part of what's difficult about this specific question is the implicit question underneath: are they actually different? Of course, the two communities tend to focus on different things and talk in different ways. But how much of this is just, "Different people being in the room as the two communities developed separately from one another meant they took a similar starting point and landed different places" is unclear. In that light, differences like "earthly" animals vs. "non-earthly" creatures, or "sapient" vs. "animalistic" are particularly interesting because to me, that says something about the people who gather under each moniker together more than it does about their experiences directly. Those differences do have some relationship to the different underlying experiences, but it's complicated. And when the history of this forum includes discussions about what "identity" means
, or what it means to identify "with" vs. "as" something
, it's not always obvious that two different people might even understand the alleged otherkin behavior of "focusing on identity" to mean different things.
In my experience so far, the way therians talk about things and where they put their focus tends to make more sense to me, and are the same sorts of places I would find myself putting emphasis. I do have an experience of "animality", and that would be the main emphasis of my thoughts on this subject, so at large I find "therian" a good descriptor for myself. I don't find myself so focused on identity (at least as I interpret folks to mean when describing otherkin stuff), and when I do look at more explicitly otherkin discussion, I find it just doesn't speak so well to my experience, so I don't find "otherkin" a good descriptor for myself. But at large, figuring out whether either, both, or neither terms fits you is a process of both learning more how each community sees itself, and figuring out how you understand yourself in contrast to those visions.