First, let's not lose track of the high order bits here: the Venn diagram between these two companies is more overlap than not. Both are large-scale, consumer-facing Internet services. They both build heavily customized datacenters; contribute a lot to open source; write a lot of back-end code in C++; have intricate big-data pipelines that make their products go; solve basic problems in information retrieval; care about ad targeting; contribute research results, and PC members, to CS conferences in various disciplines; will hire every good ML person in the world if they can; and so forth.
There is consequently a lot of overlap between their employee populations. Many people have gone on from work they're proud of at Google to do work they're proud of at Facebook. Some have gone the other way, and as FB gets closer to Google's size there will be more of them in the future. Our kids go to the same schools; this is not the Bloods and the Crips. Choosing between the two is one of those "nice problems to have."
While there are lots of "little" differences, I think most are driven by two primary differences.
First: Facebook is about 10% the size of Google, in both headcount and revenue. (An interesting consequence of this, by the way, is that only about 10% as many Facebook engineers as Google engineers are reading and responding on a "smackdown" thread like this one; you should bear this in mind when skimming them.) I think my friends at Google would agree that engineers at Facebook have considerably more autonomy and responsibility, and less process obstructing the exercise of that autonomy.
Second: Google is famously pursuing many "if-you-build-it-they-will-come" tech-for-tech's-sake projects. Each project represents a small portion of Google's much larger headcount, and yields a lot in PR, recruiting, and hopefully someday in creating revolutionary consumer products. Facebook is focused on those technologies that allow humans to communicate with other humans. That problem space is plenty big, encompassing work in programming languages, databases, networking, data science, information retrieval, machine learning, etc. We leave other technical problems to organizations with other missions; they have smart people, too, who understand their problem space better than we will. This is a classic trade-off between breadth and depth; while neither company is 100% dedicated to one or the other, they have clearly chosen different spots on this continuum.
Finally, if anybody is actually wrestling with this dilemma, and would like to reach out in private, feel free to do so at Keith Michael Adams' initials @fb.com.
Well that's interesting, because I count 1 Google employee vs 5 Facebook employees. Did this thread get sent out on an internal Facebook mailing list or something? Several are new users.
We don't use mailing lists much at Facebook, preferring to use Facebook where possible. Like anybody else, Facebook employees who see something of interest on HN often use Facebook to share the link with those friends. There is nothing conspiratorial about this process; it's the same way all other links on Facebook spread through peer groups.