I have a Blogger account, but I don't use it much.
I have a Twitter account, but I don't use it much.
I have a Facebook account, and I use it more that both previous.
Twitter's concept, "What are you doing right now?", seems interesting, but has never quite grabbed me as being something I want to use to commit my activity to permanent record. It seems a bit too trivial. What are you doing right now? Well, to be honest, right now I'm writing a Tweet. Or, to be less literal, I'm sitting around doing not much. Or walking, or driving, or whatever. Not earth-shaking stuff.
Facebook's concept, "What's on your mind?", has always seemed more relevant to me. It's as if I'm sharing something with a friend in the room. Facebook is a happy medium between fluff (Twitter) and weighty (Blogger). But I think the big plus is the fact that there are so many people on Facebook. There's a critical mass of people I know in the same virtual community. So there's always something new to see, and when I post there's always someone out there who sees it.
Blogging seems to me to convey a higher threshold of content. By that I mean that blogs are used to record thought-out writings. More like essays. If Twitter is a clause, then Facebook is a sentance. But Blogger is an essay. And often I just don't feel like having to write an essay. I just want to write a few sentances.
I guess Facebook has found the right balance for me in communication. I'm not much of a texter. That's mostly because I don't have a smart phone. But also I'm not in the habit of communicating in small bursts. So maybe I would equate Twitter with texting, or IM. Then Facebook is more like email. I use email all the time. Since I'm familiar with email, Facebook is a more comfortable fit for me. Then Blogger would be like.. all I can think of is writing an essay. To me, it implies a more thought-out body of content.
Twitter: unfiltered stream of words from my mouth.
Facebook: coherent thoughts on a single subject.
Blogger: developed thoughts with a bent toward persuasive essay.
And most of the time in my daily activity, Facebook is where I'm at mentally: coherent thoughts on a single subject.