All the new brushes get covered with your active texture, which, upon loading Hammer, will always be the very first that would show up in the texture browser without any filters.
As for corners: the 45 method is considered superior since it creates the least polygons in best case and is the cleanest, espically if you've mastered vertex editing. A usual _| joint is mostly alright as it's very editable, but it does leave more polygons.