Depends on the story. Over at RavishU, I published two stories earlier this week, one in each format. The chapter based story is part of a long tale that I'm working on, while the one-off was just a quickie. Well, quickie by my standards. It was still long enough to be broken into two parts, but that's because I went over the 10k limit.
If you have a tale that's a quick in-done-out, go for it. If you think it is best served by breaking up into chapters, do it. The story will tell you.
If going by chapters, keeping them in a thread is ideal, in my opinion. Otherwise you need to link to the previous chapters, hope people that click on to read the last chapter have navigated through the previous ones, and don't get completely sidetracked along the way.