This question is a bit like asking, "which is better, apples or oranges?"
The best answer I would imagine would take into account who you would fly the most, how often you fly them and what you want to get out of your frequent flyer membership.
For instance, CX treat their own members really well, but even if you're travelling in premium classes it can be hard to get up to the top. While QF's scheme allows you to get status relatively cheaply from premium classes, but they may not treat you as well (though reports suggest that they do on CX). If your goal is to burn the earned miles for upgrades and award flight, there's a whole minefield of what can and can't be done to understand.