13 cm is the best option.
Components are better but you'll probably need to mount the tweeters higher up like the plastic bit with the mirror adjuster.
6x9's can fit but many foul the window mechanism and once you've spaced them out enough to clear the window you have to remove the speaker grille from the door card.
Just fitted a headunit in the daughters Ka and now need to do the speakers as the Ford stuff isn't up to it!
I'm just going to get a set of 13cm co-axials and make my own MDF mounting ring.
Mike