Google. I can never get over Facebook's "ick" factor. My opinion of Facebook is that it's rotten at the top; I feel it's run by morally-flexible people who will do anything for money. Technically, I don't think they're working in sufficiently diverse problem areas. Delivering status updates and plumbing ads, that's it.
Google products and projects run across the spectrum from technical to social to political. Google has research labs, it has offices in many of the developing parts of the world, it's very much involved in education.
There is absolutely no comparison: I would be proud to call myself a Googler. I run much of my private life online on Google services, and have spearheaded my company's move to Google apps & standardization on Android. Facebook? Facebook is the reason I installed the RequestPolicy plugin to block their cookies.
"Delivering status updates and plumbing ads, that's it."
Facebook's messaging, events, photos, and groups products have replaced entire classes of web products for me. I don't know how it is on the inside, but from my vantage point, it seems like there's plenty of interesting work going on there.