Pros
I worked at Harding Loevner for about half a year, and left after I discovered it wasn't a good personal fit, however I think if you click with the culture, it's a great place. Free breakfasts on Mondays, a gym on site, and a fairly lax dress code make for a very balanced environment. I was able to grow out a beard and no one batted an eye, to give you a sense of the informal atmosphere. It is a small firm and so you get to know everyone quite quickly. Pros include great exposure to the portfolio managers, very smart people, and great hours. They pay for your CFA exam which is also a perk.
Cons
You need a long term commitment to the firm, and your role may be different than what you envisioned. There is a large emphasis on earning your way to more relevant duties, however this could be said of many places.