These are my two favorite blogs of Q4`19:

Pat Collison [1] (Co-founder, CEO Stripe) doesn't blog often, but is one of the most interesting and insightful people I have ever read

I don't know much about Alexey Guzey [2] yet, but he also has some very good posts (he writes more often and more long form, and is more similar to Gwern and SSC, in part because I think those two blogs have influenced him heavily)

[1] https://patrickcollison.com/

[2] https://guzey.com/