Pros
If you have no experience, go to Marca. They have a lot of simple work than anyone can do, and you will understand what NOT to do when you leave. If you can keep your sanity here, you can work anywhere. A great gauntlet of miscomunication where no one knows how work goes out.
If you've worked in advertising before, and are looking to leave, remembering this place will keep you from coming back to advertising. The hours, the egos, the clichés are all here. Enough to have you roll your eyes of the thought of coming back.
Cons
"MANAGEMENT": Your boss is always available. Good right? It just means he's probably surfing the Internet with no clue of what's going on in his agency. Until you ask him for his opinion on whatever you've been working on. Then he'll just have you scratching your head why you asked him in the first place. Now you have your already insane work load, plus whatever wrench he threw in their at your request.