For the most part, I love macOS Sierra. It has a few quirks, but I enjoy my experience day-to-day, specially on my new 2016 MacBook Pro. The part that keeps frustrating me, was having to keep entering my passphrase for my public key, every time I tried to use SSH or do a git push/pull.
Thankfully, Rob Allen has put together a nice short guide on fixing SSH key problems on macOS Sierra. If you are a developer, and running macOS Sierra, I highly encourage you to check it out.