As an engineer who worked at both:
- Personally, I believe that Google works on bigger and more important ideas/projects than Facebook. I think it can have more positive impact on humanity in general.
- Google's engineering culture is not "move fast and break things": things get done more slowly but in general designed, coded and tested much cleaner/better. This might fit well to some people better.
- At Facebook, you typically write PHP. At Google, you typically write any of Java/JS/Python/C++. These are more widespread (and in my opinion, better) languages than PHP.
- Google has more restaurants than Facebook : )
- Breadth of product line is much bigger at Google.
- Google has a much better research department. In fact, Facebook doesn't have one.
- Google has much more learning opportunities (a lot of courses, codelabs, much better documentation and stricter code review)