As a result, I've noticed that fanfic writers, generally speaking, can be divided into six different categories. This doesn't apply to every fanfic writer ever; still, in my experience, most fanfic writers do fall into one or more of these categories.
1) Aspiring Professionals
These fanfic writers have dreams of becoming professional fiction writers one day. While they enjoy writing and posting fanfics, they do it as a way to practice their writing skills and to get feedback on their work so they can one day reach professional level. They generally appreciate lengthy, detailed reviews, even if the reviews are harsh and blunt, mostly because they want more than anything else to improve.
Aspiring Professionals are not necessarily the best writers around, but they are always striving to improve and are always trying new things. They tend to be fairly prolific and often gain a reputation in their fanfic circles for their work ethic and the quality of said work.
Surprisingly, Aspiring Professionals are few and far between in fanfic communities. This is less surprising when you consider that most fanfic writers write purely for the fun of it and have no dreams of publishing original fiction or having a writing career of any sort. Unfortunately, this sometimes causes conflicts between Aspiring Professionals and the other kinds of fanfic writers because Aspiring Professionals sometimes hold others' work to their own lofty standards and can be quite harsh in their reviews when someone else's story is not quite as good as it could be.
Sooner or later, Aspiring Professionals stop writing fanfics in order to focus on their original fiction (though whether they become actual professionals is another question entirely). Depending on how good they are and how much they are liked, this can leave a big hole in the fanfic communities in which they wrote, even if the Aspiring Professionals continue to comment on someone else's story every now and then. Then again, sometimes they leave and no one gives a darn, so like I said it depends on the quality of their work and their popularity.
I myself am an Aspiring Professional, although I have no idea if I have a reputation for producing quality work or not. Nor have I completely left the world of fanfiction, either, as I am still posting In the End and The Biological Chronicle flash fiction series.
Aside from that, though, I think the term fits me well, at least better than the others do.
To the Hobbyist, fanfiction is a fun pastime, not practice for a future in fiction writing, like how Aspiring Professionals treat it. Most Hobbyists usually do appreciate criticism, but the degree to which they do varies considerably, ranging from listening to even the harshest of criticism to ignoring/attacking anyone who points out even one small typo in their work.
To be clear, I'm not saying Hobbyists are bad writers. Oh, no. There are many good Hobbyists (in fact, some of them are on par with professional fiction writers when it comes to quality). And many Hobbyists do take their craft seriously, even if they do not write as often or produce as much work as Aspiring Professionals do.
Nonetheless, their work ethic is generally not as good as that of the Aspiring Professional. They can go months at a time without writing a single word of fanfiction and usually take an inordinate amount of time to finish longer works. If they are in the middle of writing an epic, for example, and some life crisis comes up that they can't avoid or fix immediately, they will generally drop the fic at least until the problem is dealt with, often without alerting their readers until the problem has passed.
Some Hobbyists can be quite prolific, but the vast majority aren't, although they definitely post more fics than Contestants or One-Shooters (see below). Hobbyists can also be fairly active in their fanfic communities, participating in critic's clubs or judging contests or whatever.
I'd say that most fanfic writers are Hobbyists. They write fanfiction for fun or to connect with fellow fans or to explore their favorite franchise or whatever, but their true passion usually lies elsewhere. They, too, stop writing fanfiction at some point, though unlike the Aspiring Professional, their disappearance is usually noticed less (unless they were very popular or good, that is).
A Contestant is a fanfic writer who only writes fanfics if there is a contest going on. If there is no contest, then they aren't usually writing anything even if they have some story ideas.
Like with every other type of fanfic writer, the Contestants' quality ranges from amateur to professional. They probably make up an even larger majority than Hobbyists; however, I generally do not think of them as members of the fanfiction community due to how rarely they write.
A Contestant might become a Hobbyist or even an Aspiring Professional, depending on how much they enjoyed writing their contest entry, but the vast majority do not. When they disappear, few people care because they didn't write very much (unless what they did write was exceptionally good, of course).
4) The One-Shooter
These guys generally do not write anything longer than a short story; heck, sometimes they stick solely to flash fiction. It's mostly because they are afraid of committing to longer works. These guys may have ideas for longer works, but they lack the will, discipline, and commitment necessary to see them through to the end. And if they have ever tried to write an epic-length story, then it is usually lying abandoned somewhere on the Internet and is often the reason why they stick to short stories/flash fics.
Because they stick with short stories and flash fiction, One-Shooters can be incredibly prolific, often even more than the Aspiring Professional. They're usually pretty good, too, at least when it comes to writing short fanfics.
They do great with prompts, but sometimes have difficulty in coming up with original ideas as a result. I'd say these guys make up a sizable minority in most fanfiction circles, but the extent to which they do varies from community to community.
An uncommon group, Collaborators rarely work on their own. They prefer to write fics with at least one other writer, sometimes with more than one. Failing that, they may rely heavily on multiple beta readers for feedback and ideas in their works.
Collaborators generally put out much less work than non-Collaborators, mostly because they are working with another writer, which almost always increases the amount of time it takes to finish a fic. Their epic-length stories generally remain unfinished mostly due to the challenges of working with another writer.
Like I said, they're not very common at all, so it can be hard to gauge the quality of their work. Nonetheless, I've seen enough Collaborators in fanfiction that I figure they deserve a category all their own.
6) One Fic Wonder
Pretty self-explanatory. These guys write one fic--sometimes an epic, sometimes a short story (though usually a short story)--that becomes suddenly popular, akin to the kind of unexpected successes in original fiction (such as Harry Potter, Twilight, or any other breakout series).
After the initial buzz dies down, though, these guys often disappear. Most of the time it's because, like Hobbyists, their true passion lies outside writing and so generally do not try to follow up their big hit with another story.
When they do write another story, it usually isn't as popular as the original even if it's just as good if not better. Some of these One Fic Wonders, as I call them, do go on to write more fanfics, maybe even become Aspiring Professionals, but that is rare and does not always happen.
These are the six different kinds of fanfic writers I've noticed over the years. These categories aren't mutually exclusive (you could be a One Fic Wonder Contestant, for example, or a One-Shooter Aspiring Professional or whatever), nor does being one type mean you'll always stay that type (a Hobbyist could become an Aspiring Professional and a One Fic Wonder could become a Hobbyist). And of course, they don't cover all fanfic writers (although I have a hunch that they cover most of them).
To be clear, I am not asserting these categories as the undisputed, undebatable Truth or whatever. I am merely sharing my observations to see what everyone else thinks.
Do you agree? Disagree? Notice any other types that don't fit into any of the six I mentioned above? Share your thoughts in the comments.