If you remember, I participated in NaNoWriMo 2011. That pretty much inspired me to get back into writing regularly (my awful writing ability ignored), so after searching for things like "teen writing" and "writing sites", I found Figment. I've also been a member of Wattpad for some time, so now, I feel like comparing the two sites.
Note that I'm ignoring the genre of fanfiction on both sites, because I think fanfiction belongs on fanfiction.net
I do like the messaging system, where you can have private messages to a user, something Figment lacks.
It also has an app, which is really useful for reading. I don't really care how good a mobile browser is, for writing and reading, I prefer dedicated apps. Plus, something goes wrong whenever I try to read a story of Figment, because it loads in about one-third of my screen.
For forums, Wattpad wins. That's because Wattpad will notify you if someone replies, unlike Figment. In Figment, I can't even keep track of what I've commented on.
I like the covers. I know a lot of people prefer Wattpad's cover functions, but to be honest, I had a lot of problems with it. I'm not very good with art, but I don't like the default cover of Wattpad, so I normally try to make my own. Unfortunately, I can't upload some of them, no matter what. I don't understand it at all. At Figment, I do like the alternative covers (besides the Default, which you can choose) and the (limited) customisation. I haven't felt the need to make my own covers yet, which suits me perfectly.
I also think the groups are better. I'm not sure how Wattpad's groups work even now, but I like Figment's clearly defined groups.
Lastly, the voting system, although I think that's personal preference. Basically, I like that in Figment, people can give a reaction as well as a vote. I think it helps you to see if your story succeeded. I mean, if your story is popular, but everyone gives it "laugh" instead of the "cry" you were aiming for, you can be sure your story missed the mark.
My first and most important reason - I've made friends on figment! Despite the fact that you can only communicate by commenting on each other's wall, I've made friends who cheer me on. It's so encouraging.
This is shallow, but I just like the design of the Figment site better. There's no reason for it, but the whole thing, from the colour scheme to the preview to the actual showing of stories, just appeals to me.
I like the stories on Figment better. There, I've said it. I know there are a bunch of different stories on Wattpad, but the "hot" stories on the front page are normally the same type. Unfortunately, it's the type I don't read. On Figment, the promoted stories change according to the time of year, which already makes it more diverse than Wattpad's.
There are also people who don't like the competitions on Figment, but I actually think it's cute. I don't enter, but if I ever wanted too.... well, more than the competitions, I like how it's tied up with popular YA books.
Lastly, I'm getting more reads on Figment. I do about the same amount of effort on each (at least when I was first on Wattpad), but somehow, I have more reads, comments in Figment. I felt ignored in Wattpad, but I do feel welcome in Figment. Which is why I'm on Figment a few times a day now (and reading so much!) while I haven't touched Wattpad in a while.
So in conclusion, I think it's mostly a matter of personal preference. I think it's really great that there's a bunch of writing sites on the Internet so you can find the one that fits. What about you? Where are you on?