Pros
Great salary and corresponding benefits. Well-defined, collaborative culture. A lot of agencies will say that, but few genuinely follow through with dedicated programs focused on mentoring/developing staff, professional development stipends and a genuine opportunity to "choose your own adventure," so to speak. All levels are encouraged to speak up early and often about the type of clients they want to work with, and the type of work they want to do (client management, media-first focus, content creation, etc.). Beyond that, they make a point to hire an eclectic, smart, driven bunch -- many of whom have fairly atypical backgrounds for the typical PR firm, which is quite refreshing. It's a group that genuinely enjoys working with one another overall, which makes all the difference. But this is all table stakes. There's a quarterly beer pong tournament that takes place across both the SF and NYC offices! Win, and your name will be immortalized on the plaque at the base of a giant, plastic trophy that sits prominently in the SFO office lobby.
Cons
Like any agency, you've got to balance a demanding workload across a diverse client base. It can be stressful at times, when multiple clients are working on big projects -- but by and large, the support structure is there and there's a great camaraderie that helps mitigate this.