C-a conflicts with bash's move to start of line. Not everyone would care, but that's one of the few bash shortcuts I personally consider important.

I can't stand the default C-b either, it feels like an awkward reach to me and makes tmux seem to require way too much chording.

I've recently switched to using C-j, which duplicates the enter key. I also changed next and prev page from n / p to C-n / C-p. That way I can fly through my tabs with a single press & hold on the Ctrl key. So much nicer.