Pros
Slingshot has the best of both worlds -- big enough to have best-in-class resources, and small enough to make a personal impact. I've worked at a 10-person agency in Austin, and at a 700+ person agency here in Dallas, and after more than 7 years now here at Slingshot, I can say I truly love the mid-size. Slingshot has sophisticated resources (literally everything a media person could want...MRI, almost all modules of eTelmar, Kantar Stradegy, SRDS, eMarketer, DOMO dashboarding, the full suite of Nielsen Online (@Plan, AdRelevance, VideoCensus, NetView, MobileNetView, you name it), The Media Audit...plus also Mintel, iconoculture, and Crimson Hexagon) you'd expect in a huge agency, yet with only about 80 employees, you can really be entrepreneurial and voice your opinions and recommendations for clients. Plus, you get a ton of responsibility early on, with client-facing visibility early. If you're ready for more, they'll give it to you! I've had the pleasure of moving up in my department to a leadership position, rarely with someone else vacating a position. Slingshot does a great job of moving people along their career paths without being "tied to an org chart." This is great for people who are self-starters, can take the initiative and manage themselves well, and who have the drive to succeed. It's also highly collaborative. What's perhaps best of all though, is the "almost weird" level of cameraderie and familial-like spirit here. There's literally NO internal competition (not like in other agencies). The teams really have each others' backs and pitch in to help each other. I'm thankful for the great group of people I work with! At the end of the day, it's the people that make this place great. (Weekly beer carts and the charitable foundation don't hurt either! Not to mention pretty darn good healthcare.)
Cons
With a bunch of entrepreneurial type people, comes the desire sometimes to "reinvent the wheel" a bit too often. Adhering to "process" can be a bit cumbersome, and sometimes we get in our own way. Generally I'd say that is driven by passion and enthusiasm, but we could improve at running a bit more efficiently. Also, we tend to be pretty lean on our teams, and so the hours can be a little longer than what we'd like to see. (That said, senior management has been receptive to hiring additional headcount when we need to do it.) Not a ton of cons overall though!