I use Emacs on and off, as well as Vim, and the key I've settled on for tmux prefix is ^q. It doesn't conflict with anything useful (that I've found anyway) and it's easy to hit with a caps lock as control.
For the record ^b is also move backwards by character in basic readline bindings (so it works in Emacs, on the command line, and everywhere on OS X). I've always found it baffling the programs like tmux and screen override readline bindings. Shouldn't those be on the list of bindings to never override?
For the record ^b is also move backwards by character in basic readline bindings (so it works in Emacs, on the command line, and everywhere on OS X). I've always found it baffling the programs like tmux and screen override readline bindings. Shouldn't those be on the list of bindings to never override?