Pros
I used to work in Big 4, and comparatively speaking, BDO works less hours and at a lower stress level...all while making the same in salary. There is a regional firm feel to my office, but I am getting experience at a national level. Flexibility is great, and the people are friendly. There are a lot of office activities to keep employees engaged. You don't feel like an anonymous face in the crowd like at Big 4. The relationship from the staff level to the partner level is dynamic. I feel comfortable enough to walk into a partner's office and shoot the bull with him or her for no reason.
Cons
The calibre of clients are not that of Big 4, both in diversification and quality. In my office, travel is more extensive than my previous firm.