For me the best way to have an accessible ESC key is just to use Alt-h, Alt-j, or just pressing Alt with any normal mode key. It will work on any vim installation out of the box, it is easily accessible and doesn't require remapping.
As long as your terminal is configured to send the Meta modifier as an ESC prefix rather than a shift bit, and as long as your Alt key serves as Meta.
I've set my capslock to be escape and my alt to be control. I don't know where my alt is, but I've never really used it. (I think the only usecase for alt is Alt-Tab to switch windows, but that always feels epically unpredictable to me. What's going to happen? ... I prefer just clicking on the window I want).