If I had to choose just one blog or a twitter account for that hypothetical deserted island question(what is the one x-item you'd choose if stranded on a deserted island?), it would be that of John Baez without a second thought. His personal blog and tweets are absolute treasure troves for anyone interested in Math.

https://johncarlosbaez.wordpress.com https://twitter.com/johncarlosbaez

The recent breakthrough in finding the smallest Lebesgue cover [1] was triggered by one of his blog posts about it a few years back.

1 -- https://www.quantamagazine.org/amateur-mathematician-finds-s...