Which of these aspects would you rate as the most important when it comes to branding?

I would say designing because you have to put some thought and even do some research before you launch your brand. There's no use spending all your time, effort, and money marketing something that is ill-conceived to begin with.

You want to get your "ducks" in order before you go spreading your brand across the hemisphere because that saying that you don't get a second chance at a first impression is true. So get your branding down, design it well, and then market the heck out of it. :-)

Without Marketing, the other three never get seen.

I think it's Marketing

Marketing is the most important aspect when it comes to branding.

I think "Marketing" is the most important think in any kind of branding..

I would say that the most important factor in branding is consistency. Take some time to decide what your brand would look like and make sure that it says what you want it to say. Sleep on it before you make your final decision... Then stick with your brand consistently. The tough part is when you review it 6-12 months down the road is not wavering.