If you use your terminal all day, do yourself a favor and learn readline shortcuts [1]. Once you have you might stop overwriting these, because imho C-a is a terrible prefix and very handy to move to the beginning of a line.
[1] http://www.catonmat.net/download/bash-vi-editing-mode-cheat-...
Too bad now I‘m mostly on Windows and miss all these shortcuts. In programs where I can edit the keymapping, I usually change ctrl + a from Select All to jump to beginning of line. I barely use Select All anyway.
IMO the biggest mistake tmux made was not using C-a by default. I don't know anybody who doesn't remap it - it's far more convenient keyboard-wise, and it sets you up for using `screen` on servers where tmux isn't installed. So go ahead and remap it.