Paxos
I have a bit of a man-crush on Leslie Lamport (and have (unsuccessfully) tried to get TLA+ to be used at every job I've had for the last five years), and I have read through both the original Paxos paper in addition to the Paxos Made Simple paper, and I'm just going to say that I still found it about five times harder to grok than Raft. Honestly the TLA+ specification of Paxos made it click more than the papers for me, but that could just be because of the repeated readings before.It's a beautiful algorithm, but Raft has the advantage of being a lot simpler.