I've taken the approach of 'learn the defaults' for vim, but on tmux that simply won't stand because the defaults have so much room for improvement.
Pretty much everything I've read on tmux suggests the - and | bindings for window splits, same goes for hjkl bindings for movement. Adding these bindings would go a long way towards standardizing tmux.
As for editors, I use vim. (With almost no customization, as others have advocated.)
C-a a. Using emacs with screen for many years, this is almost automatic for me.
Moreover, I forgot if it's the default or if I set it somehow, but in Emacs a single C-a goes back to the beginning of a line, but C-a C-a goes back to the beginning of text on the line, which is almost always what I want anyway. So I press C-a twice anyway, everywhere, and I don't have the problem you described at all :)
defbce on
defutf8 on
escape ^]^]
markkeys "h=^B:l=^F:$=^E"
setenv LANG en_US.UTF-8
startup_message off
term $TERM
Copy pasted from somewhere, i do not recall from where.
ctrl-A is now ctrl-]
This does not clashes with Emacs, ctrl-A
These days I use C-z for tmux. It works, and C-z z is easy enough to type when I want to put something in the background.