Coming from i3, I tried Amethyst for a while when I had to use a Mac at my previous job. It seems like the best solution within the constraints of OS X, but it always seemed like enough of a hack that I ended up battling both it and the real window manager, so I ended up disabling it after a few months. The focus-follows-mouse never came close to working as expected for me.

Fighting with window size, positioning, and focus is such a productivity killer. Now I'm glad to be back in a real tiling window manager.