Being an emacs user, C-a was never practical. I always set mine to ` (backtick). Except when writing shell scripts, it's surprising how little it actually comes up, and learning to type it twice when you actually want one is not hard. It reduces by 1/3rd the number of keys involved in switching "tabs" or doing other stuff.

Unlearning typing it twice for when you're not in screen is the hard part.

But C-t is a useful Emacs keybinding. I use C-z. Pressing C-z z when you want to suspend the running app is not particularly disruptive.