I think Go is a great option for this type of thing. Google originally built the language to support large projects that needed many hands, which fits right up Facebook's alley. However, I think another good option would be Rust. It fits the bill almost as well as Go does, however, the Rust community is much more hacker friendly and would appeal to Facebook devs much more so than Go's ivory tower approach. In fact, I would say that Facebook devs would love the opportunity to help make Rust something that works well for them. And the Rust community would love to have the help. Google, on the other hand, has shown that it just doesn't care much about the community and what they need.

I don't necessarily like PowerShell but since it comes on the machine and is on every machine it is convenient to use. I spend most of my time in the cloud so (almost) every machine I touch is ephemeral and fairly stock. The thing I'm most jonesing for is SSH access to the Windows console. :)

I think that, like anything else, being clear to your future self is most important. Sure, if you're writing some tight, critical loop, then go with the most performant code, but overall neatness matters. I happen to like ternary operators quite a bit but they can get a bit tricky and convoluted if you let them.