Twitter seems better for personal use. Advertising/commercial use is everywhere, and it's nice to have a tool that's relatively uncluttered where I'm not being "targeted".
There are several advantages of twitter being "a standalone 'away message' platform" over Facebook:
•It's simpler (both in its look and its goal). I don't have to worry about applications, games, polls, or whatever else people do on Facebook that isn't communicating a single, focused idea, link, or observation. To me all that stuff isn't added value, it's just more baggage.
•Following can be one-sided, whereas friending is an agreement and is based on a real-life identity. I don't need to have a pre-existing connection to follow or be followed on twitter. Because Facebook is based on who you actually are, it doesn't have a "shit my dad says" or a "yelling bird" or whatever else that's silly and entertaining unless you have that one hilarious friend.