More likely to be Facebook, since Social Circles seems to be directly competing with them, not Microsoft.
With Facebook, I just assume everything could be made public, so I don't put private info that I don't want others to know.
Google has my searches, and what I've clicked on. And good luck trying to get them to forget those logs.
Facebook may not know as much about you, but they often know much more detailed information (ie, where you were last night).
Most of Facebook's users don't consider their "wall" to be public despite the fact that Facebook defaults it to be so (and has repeatedly reset privacy settings in the past to be "more public"). Complicate this with the fact that others can "implicate" you with their messages written on your wall. Despite you hiding them, they are there, in Facebook's servers just like your Google searches... except you didn't write them.
Facebook doesn't know anything about anyone that they're not comfortable sharing with at least one other person. Google knows things about people they would never share with anyone. That's a fundamental difference, not related to privacy savvy.
Facebook does have lots of dirt people only want to share with a few people, however.
Ummm, and maybe every site you ever visited whose owners display those funny "like" buttons.
And for tracking where I've been, Facebook is no worse than any other ad agency; that they show me that they're tracking me is no worse than DoubleClick's or Google Ads' tracking.
You're only counting data given to them directly, as if the things you tell Facebook are the only things there. They also have a lot of data based on what they infer from your behavior. The most visible aspect of that would be when they recommend people for you to friend.
And then there's all the data other people give them about you. Oh, sure, you can untag the photos or whatever, but who knows if Facebook really forgets? I can just imagine the uprising if Facebook ever sorted through all the photos where the tag was removed, compared them to the tagged photos to make sure it was the right person, then started selling "X's Embarrassing Photo Collection" or something. No, they'd never do that for obvious reasons, but they still have that kind of data.
What I'm trying to say is that they have more information than you realize. I'm not saying that they will or won't do anything bad with it, just that they have it. So whether you care or not depends on how much you trust them.
For the record, Google has plenty of data, too. I personally trust Google a bit more than most companies, but that's just my opinion and it could always change.
You're still missing the point: when information is put into Facebook by me or others, the intent is to share it with others. Facebook is not a vehicle to do things in private, the entire purpose of it is to share with others, whether that be your list of connections, your photos, how much time you waste on Farmville, or how frequently you communicate with Aunt Tilly.
Facebook is the anti-privacy, it's a public space, a place to get things out in the open. There's nothing private at all about Facebook, and that's the entire point of it. It's what Tim Berners-Lee envisioned the web to be, and what it would have been had he been able to put useable authoring tools into the hands of the masses, instead of HTML being limited to the benighted few that can afford the time investment to learning it and working with a web server.
Google, on the other hand, pretends to be an ISP with implicit promise of privacy, but will exploit the fuck out of your private email recipient list just to try to do what Facebook is doing. Google's core business is the same as Facebook's, advertising, but Facebook goes about gathering data about you in a far more transparent and clear manner than Google.
When somebody gives all that juicy personal information to Facebook, they're doing it with the intent to share and are making it public of their own volition for their personal social benefit. When somebody gives personal information to Google, they're not giving their search terms to Google in order to share search terms, they're doing it get something else in exchange, but may very well wish they could keep that juicy personal information completely private.
IMHO, trusting Google more than Facebook or Microsoft or Apple is extremely foolhardy, and a testament to how far a catchy slogan can go on the PR front. It doesn't matter how well-intentioned the people at the top of Google are, failures to adhere to policy will happen, and the Buzz incident is just how flagrantly Google will fail at "not being evil" when they're desperate.
I should note that my Facebook account sits idle because of my paranoia about it. But at least everything Facebook has, I wanted to be public. Google has me by the balls.
Stuff you've shared with other people != public information. That's the whole reason Facebook exists.