Pros
I worked at Antarctic for almost two years. It is a small agency, where each employee has the opportunity to work directly with clients and other team members, and is encouraged to make decisions and present them. The portfolio of clients I worked with was diverse and interesting and I had opportunities to perform at a level of responsibility that would have been unreachable so quickly at other agency. The working environment was laid back in general, but tough and demanding when needed.
Cons
It's a small agency, and that comes with cons.