I've had the ctrl-a setup ever since migrating from screen to tmux, just due to muscle memory. But it is more conveniently located than ctrl-b - it's also rather nice if I have multiple nested layers of tmux due to temporary ones on other hosts. Sure you can just keep repeating the bind, but, just remembering that the second layer uses ctrl-b is a bit more convenient I feel. Slows me down a little, but usually I'm not using the 2nd layer as much.

I don't use capslock for ctrl though. It's much too useful as the Compose key ;)