I publish my chapters after I finished them. When I've got a lot of inspiration and I write multiple chapters I wait a couple of days until I upload the next chapter. I don't have the whole story yet, but I do have an idea on how I want the next two or three chapters to go. I try to give my chapters an ending like some TV-series do; I try to give the reader something to look forward to.
I only just started writing, so there might be better ways.
I think you just have got to do it the way you like it. If you want to write a complete story and then post it in chapters, then do that. If you want to upload chapters after you've written them, then to that.
Also, you don't always have a lot of time to write, so even though you want to finish a chapter quickly, sometimes you simply can't.