I think putting ctrl on the capslock key is the more efficient move, honestly. But Vi was designed for a machine that had esc where your tab is. It's built for efficiency but you lose all of it when you have to physically pull your whole hand up off of the home row.

The Vim wiki has a lot of tips for more efficient mappings[1], but if you don't want to be dependent on your own idiosyncratic config, ctrl-[ is literally the keycode that the physical esc key generates, and it's soooo much easier to hit there's no reason not to retrain your muscle memory to prefer it.

[1] http://vim.wikia.com/wiki/Avoid_the_escape_key

Why choose? When I hold down caps lock, it acts like CTRL. When I hit it once, it acts like ESC.

Got a tool that will do that on os x sierra? I used to us karabiner, but that's hosed by the updated until they can get elements cleaned up.

Have you tried Karabiner-elements[0]? I haven't used OS X the past few years, so I don't know if it actually works, but somebody suggested it on reddit.

[0]: https://github.com/tekezo/Karabiner-Elements

I have, it's not quite there yet ... I've been a fan of Karabiner since I first switched to mac.