I believe that advertising is the most lucrative niche in design because it is hard to e able to know what everyone is thinking. I believe that it is the most competitive and difficult because of all the people that want to get their hands in it. Like what was said in a lecture before, advertising is the most difficult because you have to know what will get people off their butt's and go but the products that you are trying to sell.
You have to e able to get into the target audience heads and sell them the product that you are advertising. You have to make people remember you either by making them laugh or by making them react to your advertisement with an emotion, whatever that emotion might be.
This is what makes advertising the most competitive and difficult for people to master. Or at least it is what I think about this area of design.